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© 2003 American Society for Clinical Oncology Prognostic Significance of p53 Mutation and p53 Overexpression in Advanced Epithelial Ovarian Cancer: A Gynecologic Oncology Group Study
From the Division of Gynecologic Oncology, Duke University Medical Center, Durham, NC; Gynecologic Oncology Group Statistical and Data Center, Roswell Park Cancer Institute, Buffalo, NY; Quest Diagnostics Nichols Institute, San Juan Capistrano, CA; and the Ohio State University, Division of Gynecologic Oncology, Riverside Methodist Hospital, Columbus, OH. Address reprint requests to GOG Administrative Office, Four Penn Center, Suite 1020, 1600 John F. Kennedy Blvd, Philadelphia, PA 19103.
Purpose: The prognostic significance of p53 mutations and overexpression in advanced epithelial ovarian cancers was examined in primary tumors from 125 patients participating in a Gynecologic Oncology Group randomized phase III treatment protocol. Patients and Methods: Mutational analysis of p53 was performed in RNA or genomic DNA extracted from frozen tumor. An immunohistochemistry assay was used to detect p53 overexpression in fixed tumor. Results: There were 81 patients (74%) with a single mutation, three patients (3%) with two mutations, and 25 patients (23%) lacking a mutation in exons 2 to 11 of p53. Although most mutations occurred within exons 5 to 8, mutations outside this region were observed in 11% of patients. A mutation in exons 2 to 11 of p53 was associated with a short-term improvement in overall survival and progression-free survival. Adjusted Cox modeling demonstrated a 70% reduction in risk of death (P = .014) and a 60% reduction in risk of disease progression (P = .014) for women with such mutations. However, these striking risk reductions increased over time (P < .02) and eventually disappeared with longer follow-up. Overexpression of p53 was observed in 55 patients (100%) with only missense mutation(s), seven patients (32%) with truncation mutations, and eight patients (40%) lacking a mutation in exons 2 to 11. Overexpression of p53 was associated with tumor grade but not with patient outcome. Conclusion: Alterations in p53 are a common event in advanced epithelial ovarian cancer. A mutation in p53, but not overexpression of p53, is associated with a short-term survival benefit. Additional studies are required to define the roles that p53 plays in regulating therapeutic responsiveness and patient outcome.
THE p53 GENE is a multifunctional tumor suppressor that is often altered in ovarian and other cancers.1–4 The p53 gene encodes a zinc-binding protein with sequence-specific transcriptional activity and 3'-5' exonuclease activity.5–15 p53 normally interacts with a variety of proteins involved in transcriptional regulation, DNA repair, cell-cycle progression, apoptosis, and proteosome-mediated protein degradation.5–20 Although the biologic and clinical roles that normal and altered p53 play in cancer remain areas of intense investigation and debate, a number of studies have shown that alterations in p53 are either associated with or not associated with patient outcomes, such as response to therapy or survival.4,21–38 During cancer development, p53 can be altered by mutation, loss, or silencing of the p53 gene as well as by transcriptional or posttranscriptional mechanisms. Thus far, missense mutations in p53 are very common in cancer cells. Nonsense mutations, insertions, and deletions in p53 have also been observed. A missense mutation results in a single amino acid change, and this type of point mutation in the DNA-binding domain of p53 (exons 5 to 8) can encode a protein that is transcriptionally inactive or that displays altered transcriptional activity compared with normal wild-type p53. Although normal cells generally have a low level of p53 protein as a result of the relatively short half-life of the wild-type protein, a missense mutation in the p53 gene often encodes a protein product that is resistant to degradation, and as a result, mutant p53 protein accumulates in the nucleus. An immunohistochemistry assay can be used to detect overexpression of p53 protein. Truncated forms of p53 result from an insertion, a nonsense mutation that generates a stop codon, or a deletion in the p53 gene, and these truncation mutations encode proteins with distinct functional activity or no activity compared with wild-type p53.39,40 Unlike a missense mutation in p53, the truncation mutations are generally not thought to increase p53 protein stability. Mutant p53 proteins that are deficient in certain or all p53 functions can complex with and inactivate wild-type p53 present in the cell. This dominant negative activity can alter the behavior and fate of the tumor cell and is thought to promote the progression of many types of cancer. Studies by the Gynecologic Oncology Group (GOG) and others have indicated that overexpression of p53 protein, which presumably reflects the presence of a missense mutation, is associated with somewhat worse survival in advanced ovarian cancers.23–28,41 It is clear that the frequency of overexpression is significantly higher in advanced-stage III/IV disease (40% to 60%) compared with stage I disease (10% to 20%). Some have interpreted the higher frequency of p53 overexpression in advanced stage patients as indicative of this being a late event in ovarian carcinogenesis. Alternatively, it is possible that p53 overexpression may be associated with an aggressive phenotype that is associated with more rapid spread of disease. In addition, it has been shown that p53 plays a role in inducing apoptosis in response to chemotherapy-induced DNA damage,25,26 and some in vitro ovarian cancer studies have indicated that loss of p53 confers chemoresistance.29–33 In the presence of intact p53, chemotherapy is followed by growth arrest and the opportunity for DNA repair. However, if repair is sensed to be inadequate, p53 may activate an apoptotic pathway. Cancers that lack functional p53 will likely vary in their ability to use alternative pathways to inhibit cell-cycle progression to allow repair of DNA damage or to undergo chemotherapy-induced apoptosis. Furthermore, cancers with functionally inactive p53 may not only be resistant to chemotherapy-induced apoptosis, but they may also exhibit a more aggressive phenotype because of an altered ability to repair mutations in genes required to prevent or promote ovarian cancer progression. Because alteration of the p53 gene is the most frequent genetic event described to date in advanced ovarian cancers, we sought to characterize more completely the spectrum of mutations in the entire coding region of the p53 gene and simultaneously examine immunohistochemical overexpression of p53 protein in a large number of stage III and IV epithelial ovarian cancers. The concurrent analysis of p53 mutation and immunohistochemical overexpression of p53 would then allow us to examine the association between these two measures of p53 in advanced epithelial ovarian cancer. The specimens for this study were obtained from a large cohort of women with advanced epithelial ovarian cancer who participated in the GOG specimen banking protocol (GOG 136) and one of two prospective, randomized, phase III clinical trials conducted by the GOG. The two treatment trials, referred to as GOG 114 and GOG 132, compared different types of platinum- and/or paclitaxel-based front-line chemotherapy. The availability of specimens that were linked with detailed clinical information, including long-term follow-up, was a major strength of this study because it enabled us to determine whether either type of p53 alteration (mutation or overexpression) was associated with demographic and tumor characteristics or was predictive of patient outcome. The ultimate goal of this type of translational research is to determine the potential prognostic relevance of a biomarker like p53 in a relatively uniform population of women with advanced epithelial ovarian cancer receiving relevant types of front-line therapy with the hope of generating testable hypotheses for future clinical trials to improve the clinical management of this deadly disease.
Tumor Specimens The GOG Tissue Bank provided pretreatment frozen tumor specimens from 125 women with newly diagnosed advanced epithelial ovarian cancer who consented to participate in the GOG specimen banking protocol (GOG 136) and one of two randomized phase III treatment protocols for patients with advanced epithelial ovarian cancer conducted by the GOG (GOG 114 or GOG 132). Specimens were collected at the time of the primary debulking surgery and were linked to clinical data resulting from the clinical trial. The laboratory assays to evaluate the presence and type of mutation in the p53 gene or overexpression of p53 protein were performed without knowledge of the clinical data and outcome. Sixty-four tumor specimens came from patients enrolled onto GOG 114. These patients had previously untreated, optimally debulked, stage III disease in which the maximum diameter of residual tumor nodules was less than 1 cm. Women on GOG 114 were stratified by whether or not they had macroscopic residual disease after their initial staging surgery and were randomly assigned to one of the following regimens: six cycles of cisplatin (75 mg/m2) and cyclophosphamide (750 mg/m2), six cycles of cisplatin (75 mg/m2) and paclitaxel (135 mg/m2), or two cycles of carboplatin followed by six cycles of cisplatin (100 mg/m2) and paclitaxel (135 mg/m2). The remaining 61 tumor samples were from patients enrolled onto GOG 132, a study involving patients with suboptimally debulked (> 1 cm diameter residual disease) stage III or IV disease. Patients on GOG 132 were stratified by whether or not they had clinically measurable disease after their initial staging surgery and were randomly assigned to six cycles of cisplatin alone (100 mg/m2), paclitaxel alone (200 mg/m2), or the combination of cisplatin (75 mg/m2) and paclitaxel (135 mg/m2).
Mutational Analysis of p53 A commercial kit (QiaAMP Tissue Kit; Qiagen, Santa Clarita, CA) was used to extract genomic DNA from approximately 50 mg of powdered tumor tissue for the 16 tumors that yielded less than 25 µg of high-quality RNA for testing. Sufficient high-quality DNA was readily extracted from 15 of these tumors, and mutational analysis of exons 4 to 8 of p53 was performed. Exons 4 through 8 of the p53 gene were amplified using primers that flanked exons 4, 5, 6, 7, and 8. The resulting PCR products were then sequenced and analyzed as indicated above. It was not possible to extract a sufficient quantity of high-quality RNA or DNA from one tumor for testing. Therefore, mutational analysis within the coding region of p53 (exons 2 to 11) was available for 109 tumors; whereas, mutational analysis within the highly conserved DNA-binding domain of p53 was available from 124 tumors (from 109 tumors that yielded high-quality RNA and from 15 tumors that provided high-quality DNA for testing).
Immunohistochemical Detection of p53 Individual sections were evaluated by two of the authors (A.B. and L.H.) using a double-headed microscope to evaluate antibody specificity and the fraction of tumor cells that reacted with the D01 antibody (exhibited brown staining). Sections of advanced ovarian cancer that failed to exhibit any brown staining were scored as negative for p53 overexpression. However, sections with brown staining were classified as positive for p53 overexpression, and these sections were further divided into those with limited (< 30% p53-positive tumor cells) or extensive (> 30% p53-positive tumor cells) overexpression. The immunohistochemistry assay was repeated in tumors that exhibited limited overexpression to determine the reproducibility of the results.
Statistical Methods
Clinical Characteristics of the Cohort The specimens used for this translational research study were obtained from women with newly diagnosed advanced epithelial ovarian cancer who consented to participate in the GOG specimen banking protocol and one of two GOG prospective randomized phase III clinical trials. The clinical characteristics of these 125 women are listed in Table 1  . The average age of the women at the time of enrollment onto their treatment study was 60 years, and over 90% of the women were white. Thirty-six percent of the participants had an initial performance score, as described by Zubrod, of 0, indicating that they were asymptomatic; whereas, 64% of the women had a score of 1 or 2, which indicated that they were symptomatic and either fully ambulatory or in bed less than 50% of the time, respectively. The distribution by histologic type was as follows: 66% serous, 13% endometrioid, 11% mixed, 5% clear-cell or mucinous, and 5% other; and the distribution by histologic grade was: 10% well differentiated (grade 1), 37% moderately differentiated (grade 2); and 54% poorly differentiated (grade 3). These advanced ovarian cancer patients received various first-line chemotherapy regimens, including cisplatin/paclitaxel (45%), carboplatin plus cisplatin/paclitaxel (22%), high-dose cisplatin (15%), high-dose paclitaxel (13%), or cisplatin/cyclophosphamide (5%). The cisplatin/paclitaxel combination was the only regimen that was provided in both clinical trials. Many patients also received various second-line chemotherapy regimens at relapse, but these regimens were not specified by protocol. At the time the data was analyzed, the median follow-up time for the 33 patients who were still alive at last contact was 87 months (range, 12 to 108 months), and there were 19 patients (15%) who were alive with no evidence of disease progression, 14 patients (11%) who were alive with disease progression, and 84 patients (67%) who had died from disease. Of the eight remaining patients (6%), one death was attributable to therapy, and the other patients died as a result of other causes.
Spectrum of Mutations in the p53 Gene in Advanced Epithelial Ovarian Cancers Mutational analysis within exons 2 to 11 of the p53 gene was performed in the 109 frozen ovarian tumors (87%) that provided at least 25 µg of high-quality RNA for testing, and 84 of these cancers (77%) displayed a mutation within exons 2 to 11 of p53 (Table 2 ). Table 3 indicates that 81 tumors exhibited a single mutation, and three cancers had two distinct mutations. Although mutations were not identified in exons 2, 3, or 11, mutations were frequently observed within exons 5 to 8 of p53, which encode the highly conserved DNA-binding domain of this transcription factor, the zinc fingers (loops L1, L2, and L3). The zinc fingers coordinate metal binding and the 3'-5' exonuclease activity associated with DNA repair. There were also 12 tumors (11%) that exhibited a mutation outside of exons 5 to 8 of the p53 gene that would have been missed if the entire coding region of this gene had not been sequenced. When this data was categorized by frequency and type of p53 mutation, 56 cancers (51%) displayed a single missense mutation, two cancers (2%) had two distinct missense mutations, 25 cancers (23%) had only a truncation mutation, and one cancer (1%) had both a missense and truncation mutation. Most of the mutations within exons 5 to 8 were missense mutations, whereas those identified outside exons 5 to 8 were primarily truncation mutations (insertion, nonsense mutation, or deletion). A majority of the mutations that occurred within exons 5, 7, and 8 were missense mutations, whereas truncation mutations were the more common type of mutation observed within exon 6.
Given the functional importance of the DNA binding domain of p53 and the availability of mutational data for exons 5 to 8 of p53 in 124 of the 125 ovarian cancers, a summary of these results is provided in Table 2  . Of the 124 cancers tested, 75 (60%) cancers exhibited a mutation within exons 5 to 8 of p53 (Table 2). There were 72 tumors that displayed a single mutation, and three cancers (2%) had two mutations in the p53 gene. When evaluated by frequency and type of p53 mutation, 55 cancers (44%) had one missense mutation, two cancers (2%) had two missense mutations, 17 cancers (14%) had one truncation mutation, and one cancer (1%) had both a missense and truncation mutation in the DNA-binding domain of p53.
Immunohistochemical Overexpression of p53 in Advanced Epithelial Ovarian Cancer
Relationship Between p53 Mutations and Overexpression in Advanced Epithelial Ovarian Cancer
Association Between Alterations in p53 and Clinical Characteristic The association between a p53 alteration (mutation or overexpression) and clinical characteristics was examined in the 109 tumors evaluated for a mutation in the coding region of p53, the 124 tumors evaluated for a mutation in the DNA-binding domain of p53, and the 110 tumors evaluated for p53 overexpression. A mutation within exons 2 to 11 of p53 was associated with histologic subtype (P = .018) but not with patient age, initial performance score, tumor stage, tumor grade, amount of gross residual disease, or type of therapy (Table 5 ). A mutation within exons 5 to 8 of p53 was associated with histologic subtype (P = .008) as well as poorer initial performance score (P = .036). Table 6 shows that p53 overexpression (tumors with limited or extensive immunohistochemical staining) was often associated with poorer initial performance status (P = .037) and lower histologic grade (P = .018). However, no association was observed between extensive p53 overexpression and any of the patient or tumor characteristics evaluated (data not shown).
Association Between p53 Mutation and Overall Survival We hypothesized that cancers with functionally inactive p53 would not only be resistant to chemotherapy-induced apoptosis, but they might also exhibit a more aggressive phenotype because of an altered ability to repair mutations in genes required to prevent or promote ovarian cancer progression. To explore the validity of this hypothesis, the Kaplan-Meier method and Cox regression analysis were used to model the time to death for patients with a mutation compared with patients who lack a mutation in exons 2 to 11 of p53. The survival plots presented in Fig 1 indicate a short-term survival advantage and not the disadvantage expected for women with a mutation in the coding region of p53 compared with women without a mutation in exons 2 to 11 of this gene. The median survival time (± SE) was 41 ± 4 months for women with a mutation within the coding region of p53 compared with 24 ± 3 months for women lacking a mutation in exons 2 to 11 of p53. The survival benefit associated with a mutation in exons 2 to 11 of p53 was limited in duration and eventually disappeared with longer follow-up. A similar short-term survival advantage was observed when the patients were categorized as having ovarian cancer with a mutation in exons 5 to 8 of p53 compared with patients lacking a mutation within the DNA-binding domain of this gene (data not shown).
The asymmetric shapes of these survival functions indicates that the hazard associated with mutation status was not proportional over time. The cross-product of the variable for p53 mutation and survival time in years was incorporated in unadjusted and adjusted Cox regression models to determine the appropriateness of the proportional hazards assumption. This testing provided evidence of an increasing trend over time in the hazard ratio associated with a mutation within exons 2 to 11 (unadjusted model, P = .020; adjusted model, P = .017) or exons 5 to 8 (unadjusted model, P = .067; adjusted model, P = .023) of p53. Therefore, it was necessary to include this cross-product (interaction) term in the final Cox regression models to accommodate the nonproportional hazards associated with a mutation in p53 (Table 7 ). A mutation in exons 2 to 11 of p53 compared with no mutation in the coding region of p53 was associated with a 70% reduction in the risk of death for women with primary advanced epithelial ovarian cancer [hazard ratio (HR) = 0.3; 95% CI, 0.1 to 0.8; P = .012] that incrementally increased over time (P = .020). After approximately 2.5 years from primary diagnosis, there was no longer any reduction in the risk of death for women with a mutation compared with women without a mutation in exons 2 to 11 of p53. Adjustments for patient age, tumor stage, amount of gross residual disease after primary cytoreductive surgery, and type of front-line therapy did not alter the reduction in the risk of death (HR = 0.3; 95% CI, 0.1 to 0.9; P = .034) that, again, increased over time (P = .024) for women with a mutation in the coding region of p53. Adjusted Cox modeling also demonstrated that a mutation within exons 5 to 8 of p53 compared with no mutation within the DNA-binding domain of p53 was associated with a reduction in risk of death (HR = 0.4; 95% CI, 0.2 to 0.96; P = .039) that increased with time (P = .041).
Association Between p53 Mutation and Progression-Free Survival Given the potential confounding impact of salvage therapy on the survival of women with advanced ovarian cancer, Cox regression analysis was performed to model the time to disease progression for patients with mutations compared with patients without a mutation in exons 2 to 11 of p53 (Table 7 ). A cross-product term for progression-free survival time in years and mutation status was needed to accommodate the nonproportional hazards that were observed. A mutation in exons 2 to 11 of p53 compared with no mutation in this coding region of p53 was associated with a 70% reduction in the risk of disease progression (95% CI, 0.1 to 0.7; P = .004) that incrementally increased over time (P = .005). The reduction in the risk of progression was only apparent during the first 17 months from the primary diagnosis. This same type of short-term reduction in the risk of disease progression was observed for a mutation in exons 2 to 11 (Table 7) or a mutation just within exons 5 to 8 (data not shown) of p53 even after adjusting for patient age, tumor stage, the amount of gross residual disease, and the type of front-line therapy.
Association Between p53 Overexpression and Patient Survival
This study reports the prognostic value of p53 mutation and p53 overexpression in tumor tissue from a relatively large cohort of women with advanced epithelial ovarian cancer. Sufficient high-quality tumor tissue was available for mutational analysis within exons 2 to 11 of p53 in 109 tumors (87%), for mutational analysis restricted to exons 5 to 8 of p53 in 124 tumors (99%), and for immunohistochemical assessment of p53 overexpression in 111 tumors (89%). p53 mutations were demonstrated in more than two thirds of the advanced epithelial ovarian cancers sampled. Although the majority of mutations were missense changes clustered in exons 5 to 8, approximately 11% of mutations resided outside of these regions and would have been missed if only the DNA-binding regions were sequenced. Most of the mutations in these outer exons predict for truncated proteins that likely differ from normal wild-type p53; they also predict for mutant p53 proteins that result from a missense mutation in their ability for transactivation, protein-protein interactions, tetramerization, nuclear export, or binding to damaged DNA. There was also a high correlation between a missense mutation in p53 and overexpression of p53 protein. Overexpression of p53 was also observed in about one third of tumors that exhibited only a truncation mutation. This may reflect stabilization of p53 as a result of altered binding with other nuclear proteins; or perhaps some p53 truncation mutants have intrinsically increased stability similar to missense mutants. However, certain truncated p53 proteins may be rapidly degraded. Although most cases with a missense mutation in p53 represented relatively homogenous tumors because greater than 75% of the cancer cells overexpressed p53, cases with a truncation mutation in p53 and overexpression of p53 protein were rather heterogeneous in the percent of tumor cells that overexpressed p53. There was an even distribution of cases with a truncation mutation that exhibited extensive overexpression of p53 (> 30% p53 positive cancer cells) compared with limited overexpression (< 30% p53-positive cancer cells). Patients with these distinct p53 profiles likely differ in their ability to use traditional as well as novel p53-dependent and p53-independent signal transduction pathways, which may promote the outgrowth of biologically distinct tumor cell populations. Furthermore, p53 was overexpressed in 11 tumors that lacked a detectable mutation in p53. Casey et al39 and Reles et al36 also demonstrated that some cancers with immunohistochemically detectable p53 do not seem to have mutations in the gene. The underlying mechanisms involved in overexpression of p53 in the absence of a mutation are not completely understood, but it has been shown that the stability of p53 is affected by interactions with cellular proteins involved in MDM2-mediated ubiquitination and degradation in the proteosome, proteolysis, and nuclear export.6,17–19,49–54 Alterations in p53 have been associated with response or resistance to chemotherapy. It has been indicated that loss of functional p53 might confer a chemoresistant phenotype because p53 plays a role in chemotherapy-induced apoptosis. In this regard, several studies have examined the correlation between chemosensitivity and p53 mutation in ovarian cancers in vitro.29–33 Some have indicated a relationship between p53 mutation and loss of chemosensitivity, but, in other equally valid studies, such a relationship has not been observed. For example, we examined six immortalized ovarian cancer cell lines, including two with p53 mutations and four with normal p53 genes, and found that the two cell lines with p53 mutations were the most sensitive to chemotherapy-induced apoptosis.55 In the current study, patients with tumors that exhibited a p53 mutation exhibited a short-term reduction risk of disease progression that indicated improved responsiveness to front-line chemotherapy. Subgroup analysis demonstrated that the improved progression-free survival during the first 17 months from the primary diagnosis was restricted to patients who were randomly assigned to receive platinum-based front-line chemotherapy with or without paclitaxel; improved progression-free survival was not observed in patients randomly assigned to receive front-line treatment with paclitaxel alone (data not shown). Consistent with this type of observation, Lavarino et al56 showed that 25 (86%) of 29 patients with mutant p53 responded to the combination of platinum and paclitaxel, whereas only nine (47%) of 19 patients who lacked a p53 mutation achieved a complete or partial response. Furthermore, Kandioler-Eckersberger et al57 examined mutations in the p53 gene and overexpression of p53 protein in breast cancer patients and reported an association between altered p53 expression and enhanced response to paclitaxel-containing therapy. However, Reles et al36 examined p53 mutations in 178 ovarian cancers from patients treated with platinum and cyclophosphamide (64%) or an unspecified front-line therapy (36%) and reported that p53 mutation correlated with early relapse of women with early- or advanced-stage ovarian cancer, but this affect was no longer apparent after the Cox regression analysis adjusted for patient and tumor characteristics. Mutations and overexpression of p53 have also been associated with poor survival in a number of studies. The p53 protein is a metal-binding transcription factor, and previous studies have indicated that prognosis was particularly poor in breast35 and colon58 cancer patients with mutations in the zinc-coordination sites within the DNA-binding domain of p53. In addition, overexpression of p53 has been shown to be associated with less favorable survival in a number of cancers. In breast cancer, p53 overexpression was associated with poor outcome in a large cohort of patients.59 Immunostaining for p53 also correlates with poor prognosis in lung60 and colorectal61 cancers. In contrast, Reles et al36 reported that neither p53 overexpression nor p53 mutation was associated with overall survival of patients with early- and advanced-stage ovarian cancer in adjusted Cox regression analysis. In the ovarian cancer specimens examined in this study, overexpression of p53 was associated with slightly worse overall survival, but this effect did not achieve statistical significance. Our study demonstrates that a mutation within the coding region of the p53 gene is associated with a short-term survival advantage, possibly reflecting an enhanced sensitivity of certain cancer cells with specific mutations in p53 to a paclitaxel-based therapy20,56,57 along with the display of a more aggressive phenotype and activation of p53-dependent or p53-independent signaling pathways as a consequence or accommodation to the alteration in p53.5–15 It is possible that because many chemotherapeutic agents damage DNA, and wild-type p53 plays an active role in DNA repair, the inability of certain ovarian cancer cells to repair chemotherapy-induced DNA damage may provide women with distinct types of mutations in p53 with a more favorable prognosis as a result of their cancer cells being hypersensitive to front-line chemotherapy. However, patients with other types of mutations in the p53 gene may no longer undergo p53-mediated apoptosis in response to chemotherapy, thus limiting the efficacy of the treatment in these patients. Furthermore, differences in sequence-specific DNA binding, transcriptional regulatory activity, and 3'-5' exonuclease activity among the mutant forms of p53 and between wild-type and mutant p535–15 may also limit the duration of the beneficial effect of a mutation within p53 by providing the cancer cells that are not initially killed by the therapy with a survival advantage. Finally, it also seems possible that some of the cancers that initially lacked a mutation within the coding region of p53 at the time of their primary cytoreductive surgery eventually developed a mutation in p53 and a hypersensitivity to salvage therapy, which might explain, at least in part, the change in the shape of the survival curve for women lacking a mutation within the coding region of p53 after the first 24 months of follow-up. The short-term survival benefit of p53 mutation was not a prospective hypothesis of this study. Nonproportionality in the effect of p53 on overall survival and disease progression was first indicated by the difference in the shapes of the Kaplan-Meier survival plots, which were subsequently evaluated using methods to test for proportional hazards. Patients with a p53 mutation had a lower relative risk of death in the first couple of years than patients lacking a p53 mutation, but the difference in the hazard ratio diminished with further follow-up. This observation is not unique for biomarker studies. For example, Gray62 reported a time-dependent hazard ratio with respect to estrogen receptor status in breast cancer patients. Specifically, estrogen receptor–negative patients had a much higher risk of recurrence in the first few of years after diagnosis than did the estrogen receptor–positive patients, but this difference diminishes over time. As new phase III clinical trials evaluate the efficacy and toxicity of platinum-based triplets and sequential doublets in the front-line setting for advanced epithelial ovarian cancer, translational research studies are required to define the role that wild-type and mutant forms of p53 play in regulating tumor response to these new combinations. Studies are also needed to determine the molecular basis for the short-term reduction in the risk of disease progression and overall survival in women with advanced ovarian cancers that exhibit a p53 mutation. Although p53 mutation and overexpression are highly correlated, they seem to provide distinct prognostic value for women with advanced ovarian cancer. Molecular and protein profiling may provide important insight into the distinct roles that normal compared with mutant forms of p53 play in regulating chemosensitivity and patient outcome by defining the changes in gene expression and signal transduction pathways that take place in tumor and host cells before, during, and after completion of therapy.
The authors indicated no potential conflicts of interest.
The following Gynecologic Oncology Group institutions participated in this study: University of Alabama at Birmingham, Birmingham, AL; Oregon Health Sciences University, Portland, OR; Duke University Medical Center, Durham; University of North Carolina School of Medicine, Chapel Hill; Wake Forest University School of Medicine, Winston-Salem, NC; Abington Memorial Hospital, Abington; Fox Chase Cancer Center; Hospital of the University of Pennsylvania; Pennsylvania Hospital; and Thomas Jefferson University Hospital, Philadelphia; The Milton S. Hershey School of Medicine of the Pennsylvania State University, Hershey, PA; University of Rochester Medical Center, Rochester; The Albany Medical College of Union University, Albany; State University of New York Downstate Medical Center, Brooklyn; State University of New York at Stony Brook, Stoney Brook; Memorial Sloan-Kettering Cancer Center, New York, NY; Walter Reed Army Medical Center and Georgetown University Hospital, Washington, DC; Wayne State University School of Medicine, Detroit, MI; University of Minnesota Medical School, Minneapolis, MN; University of Southern California Medical Center at Los Angeles; University of California Medical Center at Los Angeles, Los Angeles; University of California Medical Center at Irvine, Orange; Women’s Cancer Center, Los Gatos, CA; University of Mississippi Medical Center, Jackson, MS; Colorado Foundation for Medical Care, Aurora, CO; University of Washington Medical Center and Southwest Oncology Group, Seattle; Tacoma General Hospital, Tacoma, WA; Washington University School of Medicine, St Louis, MO; University of Miami School of Medicine, Miami; Tampa Bay Cancer Consortium, Tampa Bay, FL; University of Cincinnati College of Medicine, Cincinnati; Cleveland Clinic Foundation and Case Western Reserve University, Cleveland; Columbus Cancer Council, Columbus, OH; University of Iowa Hospitals and Clinics, Iowa City, IA; University of Texas Southwestern Medical Center at Dallas and University of Texas, Dallas; M.D. Anderson Cancer Center, Houston, TX; Indiana University Medical Center, Indianapolis, IN; Tufts New England Medical Center, Boston; University of Massachusetts Medical Center, Worcester, MA; Rush-Presbyterian-St Lukes Medical Center and University of Chicago, Chicago, IL; Cooper Hospital University Medical Center, Camden, NJ; University of Kentucky, Lexington, KY; Eastern Virginia Medical School, Norfolk; University of Virginia Health Science Center, Charlottesville, VA; The Johns Hopkins Oncology Center, Baltimore, MD; Medical University of South Carolina, Charleston, SC; University of Oklahoma Health Science Center, Oklahoma City, OK; University of Arizona Health Science Center, Tuscon, AZ; and the Eastern Cooperative Oncology Group.
We thank Fran Valvo and Caron Modeas for their excellent technical assistance in preparing this manuscript and Suzanne Baskerville for coordinating the clinical data for Gynecologic Oncology Group (GOG) 114 and GOG 132. Special thanks go to Maurie Markman, MD, and Brian Bundy, MD, for their work on GOG 114 and to Franco Muggia, MD, and Mark Brady, MD, for their efforts on GOG 132. We also thank Zoe Miner, MD, Richard Kryscio, MD, William Beck, MD, Mark Brady, MD, Gene Sobel, MD, and Brian Bundy, MD, as well as Virginia Brunetto for their comments, suggestions, and critical review of the manuscript.
This study was supported by National Cancer Institute (Bethesda, MD) grants of the Gynecologic Oncology Group (GOG) Administrative Office (No. CA 27469), GOG Tissue Bank (No. CA 27469), and the GOG Statistical and Data Center (No. CA 37517).
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Copyright © 2003 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
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ABSTRACT
INTRODUCTION
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