|
|||||
|
|
||||||
© 2003 American Society for Clinical Oncology Loss of p16 Expression Is of Prognostic Significance in Locally Advanced Prostate Cancer: An Analysis From the Radiation Therapy Oncology Group Protocol 8610
From the Radiation Therapy Oncology Group (RTOG) Genitourinary Translational Research Program, representing: Massachusetts General Hospital/Harvard Medical School Department of Radiation Oncology; RTOG Headquarters, Massachusetts General Hospital/Harvard Medical School, Department of Pathology, Boston, MA; Latter-Day Saints Hospital Department of Pathology, Salt Lake City, UT; and the departments of radiation oncology of: Fox Chase Cancer Center, Philadelphia, PA; University of California, San Francisco, San Francisco, CA; Sutter Cancer Center, Sacramento, CA; University of Rochester, Rochester, NY; M.D. Anderson Cancer Center, Houston, TX; Harper Hospital, Detroit, MI; Johns Hopkins Hospital, Baltimore, MD; and St. Joseph Mercy Hospital, Ann Arbor, MI. Address reprint requests to Arnab Chakravarti, MD; Massachusetts General Hospital, Deparment of Radiation Oncology, 100 Blossom Street, Founders House, Room 536, Boston, MA 02114; email: achakravarti{at}partners.org.
Purpose: The retinoblastoma (RB) cell cycle regulatory pathway is known to be deregulated in virtually all known human tumors. The protein product of the RB gene, pRB, and its upstream regulator, p16, are among the most commonly affected members of this pathway. We investigated the prognostic significance of both pRB and p16 expression in locally advanced prostate cancers, from patients treated on the Radiation Therapy Oncology Group (RTOG) protocol 8610. Materials and Methods: Sixty-seven cases from RTOG 8610 had immunohistochemically stained slides, judged interpretable for both p16 and pRB, available for analysis. Median follow-up was 8.9 years (range, 6.0 to 11.8 years) for surviving patients. Staining for each marker was then correlated with overall survival, local progression, distant metastasis, and disease-specific survival. Results: Loss of p16 expression, as defined by expression was significantly associated with reduced overall survival (P = .039), disease-specific survival (P = .006), and higher risk of local progression (P = .0007) and distant metastasis (P = .026) in the univariate analysis. In the multivariate analysis, loss of p16 was significantly associated with reduced disease-specific survival (P = .0078) and increased risk of local failure (P = .0035) and distant metastasis (P = .026). A borderline association with reduced overall survival (P = .07) was also evident. Loss of pRB was associated with improved disease-specific survival on univariate (P = .028) and multivariate analysis (P = .043), but carried no other significant outcome associations. Conclusion: Loss of p16 is significantly associated with adverse clinical outcome in cases of locally advanced prostate cancer.
THE RETINOBLASTOMA protein (pRB) tumor suppressor pathway has been found to be deregulated in virtually all human tumor types.1,2 The known functions of this pathway are to regulate the G1/S cell cycle checkpoint to prevent uncontrolled cellular proliferation. It has been more recently found that the pRB pathway plays an important role in apoptosis and transcriptional regulation.3 Deregulation of the pRB pathway may occur at the level of pRB itself or at the level of upstream regulators of pRB, which include the cyclin-dependent kinases (CDK) and CDK inhibitors such as p16. In the present model, CDKs can lead to phosphorylation of pRB, which, in turn, leads to its dissociation from E2F family members. Free E2F can stimulate cell proliferation, which is a hallmark of most known human tumors. CDK inhibitors such as p16 can inhibit phosphorylation of pRB, thereby preserving the integrity of the G1/S checkpoint and also suppressing the transcriptional program involved in cellular proliferation. As loss of pRB and p16 function by gene deletion, mutation, or loss of heterozygosity are quite common in human tumors and have important functional implications, we investigated whether loss of expression of these proteins, as determined immunohistochemically, was associated with adverse clinical outcome in cases of locally advanced prostate cancer. Patients in this study were treated on the Radiation Therapy and Oncology Group (RTOG) protocol 8610, a phase III trial that randomly assigned patients with locally advanced prostate cancers (T2-T4) without evidence of distant metastasis to receive goserelin (3.6 mg) every 4 weeks and flutamide (250 mg) three times a day for 2 months before radiation therapy and during radiation therapy or radiation therapy alone.4 The study opened on April 15, 1987 and closed on June 1, 1991 with a total of 471 patients; 456 of the patients were analyzed. Results from the trial demonstrated a significant reduction in local progression and a prolongation of progression-free survival for the patients receiving neoadjuvant hormonal therapy.
Study Population For this analysis, a subset of patients entered in RTOG 8610 who had sufficient pathologic material available was studied. Diagnostic material (from needle biopsies or transurethral resections) was reviewed centrally for 461 (98%) of the 471 patients, and the tumors were graded according to the Gleason criteria.5 Tissue blocks were requested from participating institutions (>100) at the time of central pathology review for all cases that were reviewed. Pretreatment serum prostatic-specific antigen (PSA) determinations were available for less than 15% (10/67) of the patients considered in this study and hence PSA was not used as an outcome parameter in this study.
Tissue Array
Immunohistochemical Technique
Definition of End Points
Statistical Analysis
Using an independent data set of 50 patients, univariate analyses were performed on both p16 and pRB to determine the best cut-point, simultaneously evaluating all four end points. Univariate comparisons using the log-rank test were performed to evaluate various cutpoints for both p16 and pRB in this independent data set. For p16, we examined the median (39), 25% quartile (25), and 75% quartile (61). We also considered a cut point of 20 based on previously published results.6 The univariate analysis showed that p16 (> 25 v Once the best cut-point was determined (using an unadjusted P value), univariate analyses of all four end points were performed. Univariate comparisons of time related end points were made using the log-rank test (Mantel). Overall survival was estimated by the Kaplan-Meier method9 and the log-rank statistic was used to test for differences.10 Because disease-specific (prostate cancer) survival, local progression, and distant metastasis are a cause-specific failure and patients could die without failing, we also performed the cumulative incidence function11 and used the Grays test to test for differences.12
Usual multivariate Cox proportional hazard models were generated to evaluate overall survival for both p16 and pRB.13 The other end points were evaluated using a proportional hazard model for the subdistribution of a competing risk.14 The models were used to determine if p16 had prognostic value after adjusting for initial treatment, Gleason score, tumor stage, and age. All factors were considered as dichotomous variables and coded as follows: protocol treatment (0, radiotherapy [RT] alone v 1, RT + hormones); grouped Gleason score (0, score 2 to 6 v 1, score 7 to 10); stage (0, T2 v 1, T3); p16 (0, > 25 v 1,
Pathologic Correlates of p16 and pRB Immunostaining Tissue blocks were obtained from 261 (55%) of the 471 patients entered in RTOG 8610. It was found that sufficient tumor material for interpretation of p16 and pRB staining was available for 67 patients. Pretreatment characteristics of the 456 assessable patients with or without p16/pRB determinations are shown in Table 1
The distribution of pretreatment characteristics by p16 and pRB are shown in tables 3 25%, but which is not statistically significant (P = .35; Fig 1A 20% (Fig 1B 25 and >25) and pRB ( 20 and >20) was assessed and found to be weak with rho = 0.12. Loss of p16 expression, as defined as 25% or less of tumor cells staining positive for p16 protein, was evident in 18 out of 67 tumors (27%). Figures 2A
Prognostic Significance of Loss of p16 Expression The univariate analysis showed loss of p16 expression ( 25%) had significantly higher risk of any death (overall survival) and death due to prostate cancer (disease-specific survival; P = .039 and .006, respectively). Relative risk of local progression and distant metastasis were likewise significantly higher for the patients with p16 expression loss (P = .0007 and .026, respectively). Figures 3A through D
The results of the multivariate analysis can be found in Table 5
Prognostic Significance of Loss of pRB Expression Loss of pRB expression, defined as pRB immunostaining evident in 20% or less of tumor cells, was evident in 54 out of the 67 tumors (80.5%). Figures 2C
The findings of this study may have important biologic and clinical implications in prostate cancer. Approximately a two-fold or greater significant increase in risk of failing for three of the four end points was observed for p16. The statistical power to detect such an increase with pRB for any end point in this study is rather low. It ranges from 45% for overall survival to 25% for local progression. Therefore, the counterintuitive finding that pRB loss is associated with a decrease in risk of disease-specific death must be interpreted with caution, given this association was not observed for other measured survival and failure end points. A future study with much larger numbers of failures to have sufficient statistical power (~90%) must be done to test this new hypothesis. From a biologic perspective, it is intriguing that reduced levels of p16 expression appear to be associated with a more adverse prognosis than reduced levels of pRB but, again, this should be viewed with some caution because of the low statistical power. According to the current paradigm of the pRB-E2F pathway, it would be predicted that loss of p16 and pRB would result in similar effects. In this light, the observed differences in predictive value between loss of expression of p16 and pRB in cases of locally advanced prostate cancer are intriguing. These observations suggest that p16 and pRB functions may not be entirely redundant in prostate cancer cells, and, indeed, there is increasing evidence supporting this possibility.15,16 It must also be considered that the CDKN2A locus that houses coding sequences for not only p16, but also for p14ARF. p14ARF has been found to prevent mdm2-mediated degredation of p53.17 Since p16 loss has been associated with homozygous deletion of the CDKN2A locus, if this were to be the underlying mechanism for the observed loss of p16 in locally advanced prostate cancer, two critical pathways would be concomittantly disrupted: the pRB and p53 pathways (via loss of p14ARF). Simultaneous inactivation of both of these critical regulatory pathways may explain the worse outcome observed with p16, as opposed to pRB loss. Second, these findings are of potential clinical significance as loss of p16 was significantly associated with adverse outcome. There is increasing data that loss of p16 may be of prognostic value in a variety of different tumor types.16,1822 Intriguingly, a recent study reported that p16 overexpression, in contrast to p16 loss, was associated with adverse prognosis in prostate cancer. In contrast to our study, Jarrad et al6 examined the prognostic value of p16 expression in prostate cancer patients treated by radical prostatectomy, not by radiotherapy. Further, the Jarrad study included predominantly patients with early-stage disease (~76% with cT1 tumors), whereas in our study, patients had predominantly locally advanced disease (~81% with cT3 disease). Hence, these conflicting results could be secondary to differences in treatment and patient population. In our study, it is notable that p16 loss remained significantly associated with increased risk of local progression and distant metastasis in the multivariate analysis, even when other important pretreatment characteristics such as Gleason grade and clinical T-stage were taken into account. The increased risk of local failure in p16-negative tumors suggests that these tumors may be more treatment-resistant (radiation ± hormone therapy) than their p16-positive counterparts. Again, it is unclear whether this is directly attributable to p16 loss or whether concomitant loss of p14ARF is the actual underlying cause. The strong association between p16 loss by immunostaining and the subsequent development of distant metastasis is also intriguing and raises interesting clinical possibilities. It has been recently found that over 50% of patients with pathologically organ-confined disease had evidence of microscopic spread of disease to the bone marrow.23 Given that a substantial percentage of patients who are staged M0 at initial diagnosis will have progression with distant metastasis at 15 years,2428 it is important to identify these high-risk patients since systemic therapy has potential value in eradicating micrometastatic disease. Although Gleason grade in its extremes does predict for distant metastasis, the vast majority of patients present with moderately differentiated tumors, which may represent a niche where a potential predictive marker like p16 may be most useful. If p16 immunostaining does, indeed, have predictive value over that of Gleason grade alone, as this study suggests, then it may have potential to be an independent prognostic marker of significance. Future studies are currently planned by the RTOG to validate this data on a larger patient population. Ideally, its predictive value must be tested not only in the context of current pretreatment parameters (eg, Gleason grade, PSA, T-stage), but also in the context of other molecular markers of potential significance.16,29,30 Understanding the precise mechanisms by which loss of p16 leads to enhanced rates of local progression and distant metastasis may also ultimately lead to the development of more effective molecular-based therapies that can enhance the effects of conventional agents in the management of patients with locally advanced prostate cancers.
This study was supported by RTOG U10 CA21661, CCOP U10 CA37422, and Stat U10 CA32115 grants from the National Cancer Institute (NCI). The contents of this manuscript are the sole responsibility of the authors and do not necessarily represent the official views of the NCI.
1. Harbour JW, Dean DC: The pRB/E2F pathway: expanding roles and emerging paradigms. Genes and Dev 14:23932409, 2000
2. Nevins JR: The Rb/E2F pathway and cancer. Hum Mol Genet 10:699703, 2001 3. Pan H, Yin C, Dyson NJ, et al: Key roles for E2F1 in signaling p53-dependent apoptosis and in cell division within developing tumors. Mol Cell 2:283292, 1998[CrossRef][Medline] 4. Pilepich MV, Krall JM, Al-Sarraf M, et al: Androgen deprivation with radiation therapy compared with radiation therapy alone for locally advanced prostatic carcinoma: a randomized comparative trial of the Radiation Therapy Oncology Group. Urology 45:616623, 1995[CrossRef][Medline] 5. Gleason DF: Classification of prostatic carcinomas. Cancer Chemother Rep 50:125128, 1966[Medline] 6. Jarrard DF, Modder J, Fadden P, et al: Alterations in the p16/pRB cell cycle checkpoint occur commonly in primary and metastatic human prostate cancer. Cancer Lett 185:191199, 2002[CrossRef][Medline] 7. Haitel A, Wiener HG, Neudert B, et al: Expression of the cell cycle proteins p21, p27, and pRB in clear cell renal cell carcinoma and their prognostic significance. Urology 58:477481, 2001[CrossRef][Medline] 8. Brambilla E, Moro D, Gazzer S, et al: Alterations of expression of RB, p16, and Cyclin D1 in non-small cell lung carcinoma and their clinical significance. J Pathol 188:351360, 1999[CrossRef][Medline] 9. Kaplan EL, Meier P: Nonparametric estimation from incomplete observations. J Am Stat Assoc 53:457481, 1958[CrossRef] 10. Mantel N: Evaluation of survival data and two new rank order statistics arising in its consideration. Cancer Chemother Rep 50:163170, 1966[Medline] 11. Kalbfleish JD, Prentice RL: The statistical analysis of failure times data. New York, John Wiley, 1980 12. Gray RJ: A class of K-sample tests for comparing the cumulative incidence of a competing risk. Ann Stat 16:11411154, 1988 13. Cox DR: Regression models and life tables. J Royal Stat Soc 34:187229, 1972 14. Fine JP, Gray RJ: A proportional hazards model for the subdistribution of a competing risk. J Am Stat Assoc 94:496509, 1999[CrossRef] 15. Rocco JW, Sidransky D: p16(MTS-1/CDKN2/INK4a) in Cancer Progression. Exp Cell Res 264:4255, 2001[CrossRef][Medline] 16. Tsihlias J, Kapusta LR, Slingerland JM: The prognostic significance of altered cyclin-dependent kinase inhibiotrs in human cancer. Annu Rev Med 50:401423, 1999[CrossRef][Medline]
17. Sherr CJ: Tumor surveillance via the ARF-p53 pathway. Genes and Dev 12:29842991, 1998 18. Hommura F, Dosaka-Akita H, Kinoshita I, et al: Predictive value of expression of p16, retinoblastoma, and p53 proteins for the prognosis of non-small cell lung cancers. Br J Cancer 81:696701, 1999[CrossRef][Medline]
19. Kratzke RA, Otterson GA, Lincoln CE, et al: Immunohistochemical analysis of the p16 cyclin-dependent kinase inhibitor in malignant mesothelioma. J Natl Cancer Inst 87:18701875, 1995
20. Kratzke RA, Greatens TM, Rubins JB, et al: Rb and p16 expression in resected non-small cell lung tumors. Cancer Res 56:34153420, 1996 21. Taga S, Osaki T, Ohgami A, et al: Prognostic value of the immunohistochemical detection of p16 expression in nonsmall cell lung carcinoma. Cancer 80:389395, 1997[CrossRef][Medline]
22. Sanchez-Beato M, Saez AI, Navas IC, et al: Overall survival in aggressive B-cell lymphomas is dependent on the accumulation of alterations in p53, p16, and p27. Am J Pathol 159:205213, 2001 23. Melchior SW, Corey E, Ellis WJ, et al: Early tumor cell dissemination in patients with clinically localized carcinoma of the prostate. Clin Cancer Res 3:249256, 1997[Abstract] 24. Bagshaw MA, Kaplan ID, Cox RC: Radiation therapy for localized disease. Cancer 71:939952, 1993[CrossRef][Medline] 25. Hanks GE, Krall JM, Hanton AL: Patterns of Care and RTOG studies in prostate cancer:long-term survival, hazard rate observations and possibilities of cure. Int J Radiat Oncol Biol Phys 28:3945, 1994[Medline] 26. Perez CA, Lee HK, Georgiou A, et al: Technical and tumor-related factors affecting the outcome of definitive irradiation for localized carcinoma of the prostate. Int J Radiat Oncol Biol Phys 26:581591, 1993[Medline] 27. Zagars GK, von Escenbach AC, Ayala AG: Prognostic factors in prostate cancer: analysis of 874 patients treated with radiation therapy. Cancer 72:17091725, 1993[CrossRef][Medline] 28. Zietman AL, Prince EA, Nakfoor BM, et al: Neoadjuvant androgen suppression with radiation in the management of locally advanced adenocarcinoma of the prostate: experimental and clinical results. Urology 49:7483, 1997[CrossRef][Medline] 29. Theodorescu D, Broder SR, Boyd JC, et al: p53, bcl-2, and retinoblastoma protein as long-term prognostic markers in localized carcinoma of the prostate. J Urol 158:131137, 1997[CrossRef][Medline]
30. Tsihlias J, Kapusta LR, DeBoer G, et al: Loss of cyclin-dependent kinase inhibitor p27Kip1 is a novel prognostic factor in localized prostate adenocarcinoma. Cancer Res 58:542548, 1998 Submitted December 26, 2002; accepted June 18, 2003.
This article has been cited by other articles:
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||
|
Copyright © 2003 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
|