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Originally published as JCO Early Release 10.1200/JCO.2003.01.128 on January 3 2003 © 2003 American Society for Clinical Oncology Prognostic Value of Circulating Melanoma Cells Detected by Reverse TranscriptasePolymerase Chain Reaction
From the Institute of Genetics of Populations, Consiglio Nazionale delle Ricerche, Alghero (Sassari); Division of Clinical Immunology, Clinical Trials Unit, Division of Medical Oncology A, and Division of Surgical Oncology B, National Cancer Institute of Naples; Institute of Pathology, University of Sassari; and Medical Statistics and Department of Dermatology, Second University, Naples, Italy. Address reprint requests to Paolo A. Ascierto, Division of Clinical Immunology, National Cancer Institute, Via M. Semmola, 80131 Naples, Italy; email: pasciert{at}tin.it.
Purpose: Factors that are predictive of prognosis in patients who are diagnosed with malignant melanoma (MM) are widely awaited. Detection of circulating melanoma cells (CMCs) by reverse transcriptase-polymerase chain reaction (RT-PCR) has recently been postulated as a possible negative prognostic factor. Two main questions were addressed: first, whether the presence of CMCs, defined as the patient being positive for any of the three markers, had a prognostic role; and second, what the predictive value of each individual marker was. Patients and Methods: A consecutive series of 200 melanoma patients observed between January 1997 and December 1997, with stage of disease ranging from I to IV, was analyzed by semiquantitative RT-PCR. Tyrosinase, p97, and MelanA/MART1 were used as markers to CMCs on baseline peripheral blood samples. Progression-free survival (PFS) was used as a unique end point and was described by the product limit method. Multivariable analysis was applied to verify whether the auspicated prognostic value of these markers was independent of the stage of disease, and a subgroup analysis was performed that excluded patients with stage IV disease. Results: Overall, 32% (64 of 200) of patients progressed, and a median PFS of 52 months in the whole series was observed. The presence of CMCs and the markers individually or combined was predictive of prognosis in the univariate analysis but did not provide additional prognostic information to the stage of disease in multivariable models. In the subgroup analysis of stage (ie, IIII subgroup), similar results were observed. Conclusion: Detection of CMCs in peripheral blood samples at the time of MM diagnosis by semiquantitative RT-PCR does not add any significant predictive value to the stage of disease. Thus, this approach should not be used in clinical practice, and further studies are required to determine its usefulness.
THE INCIDENCE and mortality rate of malignant melanoma (MM) are increasing worldwide,12 and there is a generalized need for improved methods to predict the clinical outcome of patients. Stage of the disease,3 ascertained by accounting for level of invasion,4 tumor thickness,5 and presence of lymph node or distant metastases,3 is the most widely accepted prognostic factor.6 Melanoma patients have poor prognosis because of frequent distant dissemination of the disease. Although the size of the primary lesion is frequently small, it is obvious that in many patients there has already been metastatic spread at the time of diagnosis. The detection of circulating melanoma cells (CMCs) has been proposed as a potentially effective tool in selecting patients that have a high risk of relapse at the time of the diagnosis.7 Reverse transcriptase-polymerase chain reaction (RT-PCR) can detect a single specific mRNA in a mixed cell population; thus, it can be a sensitive method for identification of circulating tumor cells.813 Tyrosinase (TYR), an enzyme that is involved in the melanin biosynthesis pathway,14 is the marker most frequently used to detect the presence of CMCs; however, its usefulness as a marker is highly debated.1521 Because the use of TYR mRNA as a unique marker could be of limited value in the management of MM patients, a multimarker assay, which includes p97 and MelanA/MART1 in addition to TYR, has been proposed to improve sensitivity and specificity of the procedure.22 We have previously demonstrated a positive association between clinical stage of MM and the detection of tumor-associated mRNAs in peripheral blood by a multimarker RT-PCR assay.23 To evaluate the clinical usefulness of such a procedure, we planned the present study to determine whether detecting CMCs by RT-PCR in a consecutive series of patients (with all stages of disease) can improve prognostic prediction, which is commonly based on pathologic and clinical prognostic factors. To explore whether circulating melanoma-associated markers can allow the detection of minimal residual disease in patients who have undergone radical surgery, we also performed analyses limited to the subgroup of patients with stage I to III disease; we also addressed the role of each of the markers individually and combined.
Patient Selection The study was conducted with a series of 200 patients referred to the National Cancer Institute (NCI) of Naples between January 14, 1997, and December 17, 1997. Patients were consecutively collected, and they were considered eligible for participation in the study if they had a histological diagnosis of cutaneous malignant melanoma, which was performed either inside or outside the NCI. In the latter situation, pathologists from the NCI reviewed the patient slides. Patients were eligible for collection of a baseline peripheral blood sample if no more than 4 weeks had passed since surgical treatment for early-stage (ie, 0 to III) disease; patients with stage IV disease (candidate for systemic treatment) had their baseline blood sample collected before starting treatment. Informed consent from each patient was sought in regard to collection of blood samples, and the study was approved by the Ethical Review Board of the National Cancer Institute of Naples. Treatment strategy for patients was not decided on the basis of the RT-PCR findings. Disease stage was coded, a posteriori, according to the American Joint Committee on Cancer (AJCC) guidelines.6 All early-stage patients were visited every 6 months after diagnosis. At each follow-up visit, a clinical history, physical examination, full cell blood count, RT-PCR assay, and blood biochemistry were performed. Instrumental assessments (ie, computed tomography, ultrasonography, bone nuclear scan) were performed if clinically indicated. Stage IV patients were followed up according to rules dictated by the chemotherapy program.
Sample Preparation and RT-PCR Assay
Statistical Analysis
Cross-tabulations and a graphic representation were used to describe the associations among the three markers. The number of positive markers for each patient was summed, producing a variable parameter (ie, the number of positive markers for each patient) that had a scoring system from zero to three. Univariate associations between markers and other baseline variables were investigated by Time-to-event analyses were performed for PFS, which was defined as the time from the date of enrollment in the study to the date of disease progression or disease-associated death. PFS curves were estimated by the Kaplan-Meier method.26 Hazard ratios of progression were estimated by the Cox model28 and are reported with 95% confidence intervals (CIs) that are either unadjusted or adjusted for stage of disease. Presence of CMCs was used as a binary (ie, yes/no) variable, and stage of disease was used as a continuous variable (ie, 0 to IV). The number of positive markers (ie, 0 to 3) was also investigated. Because of the small number of events in this study, overall survival was not considered for analysis. Taking into account that finding a prognostic value of the detection of CMCs could be crucial in the therapeutic planning of patients with localized disease (stages 0 to III), PFS analyses were performed on both the entire patient population (ie, including stage IV disease) and on the subgroup of patients with localized disease (ie, excluding stage IV disease).
A consecutive series of 200 patients diagnosed MM was studied. Patients were mostly female (58%), with a median age of 50 years (range, 40 to 60 years). According to the new AJCC/International Union Against Cancer (UICC) stage classification, almost the half of the patients had stage I disease, and approximately one quarter had stage II disease. Overall, patients without distant metastases (stages 0 to III) accounted for 88.5% of patients (Table 1
A total of 163 of the 200 patients (81.5%) had at least one positive marker; thus, they were considered positive for CMCs. p97 was the most sensitive marker, being positive in 82% (140 of 163) of CMC positive patients. Distribution of the positive RT-PCR markers is detailed in Table 2
The presence of circulating mRNA markers was significantly associated with the stage of disease. Similarly, each individual marker and the number of positive markers were associated with the stage of disease. However, no association of markers with sex and age of the patient was evident, with the exception of the presence of MelanA/MART1 and an increasing number of positive markers, which were both significantly associated with older age (> 60 years; Table 3
As of July 2001, 64 patients (32%) had suffered disease progression, with a median PFS of 52 months for the entire patient population; 46 patients (23%) had died, with a median follow-up of 44 months for living patients. In the univariate analysis, the presence of CMCs had a significant predictive value, with a hazard ratio (HR) of progression of 3.15 (95% CI, 1.26 to 7.85; P = .01) for patients with at least one positive marker (Table 4
In this article, we show that the presence of CMCs, determined by the detection of mRNAs corresponding to melanoma-associated molecular markers in peripheral blood, is significantly associated with the stage of diseasethe most commonly used prognostic system for melanoma patientsbut does not play a role as an independent prognostic factor for clinical outcome. The hypothesis that detection of CMCs could improve prognostic prediction was based on at least two issues. First, it is obvious that mobilization of cells from the site of the primary lesion through the blood stream is necessary (although not sufficient) to produce distant metastases. Thus, detection of CMCs may correspond to the identification of an early and potential step in metastatic spread. Second, many studies have dealt with the possible prognostic value of the presence of CMCs with conflicting, but mostly positive, findings. In regard to the first point, our data cannot rule out the theoretical assumption that detecting CMCs may be a signal of metastatic spread. However, physical invasion of the blood stream by tumor cells is among the earliest events in the tumor progression cascade, and many other steps are required for metastatic colonization of distant parenchymas. Detection of CMCs can be considered as a surrogate marker of such initial events for the establishment of distant metastases. However, in this case, identification of melanoma-associated transcripts in histologically negative, regional lymph nodes by RT-PCR could represent a more useful marker for staging melanoma patients than detection of CMCs, as previously suggested by our group.29
In regard to the second point, to the best of our knowledge, 15 extended papers have been published in recent years, dealing with the possible prognostic value of CMCs detected by RT-PCR on peripheral blood samples (Table 5
Altogether, there were five negative studies21,23,38,39,40 that are consistent with our findings. Time-to-event (disease-free or overall survival) analysis was not performed in any of these studies. In the larger of the studies,38 only the association of CMCs with stage of disease was tested to explore prognostic significance. Ten studies were reported with positive conclusions, in contrast to our findings. Seven of these studies did not use a multivariable statistical approach to analysis;12,15,22,31,34,35,37 thus, their results, which are consistent with our unadjusted results, cannot definitively prove the prognostic value of RT-PCR detection of CMCs. Three studies applied an analytic approach with multivariable analysis; two of them had fewer than 100 patients (the strength of their conclusions being overcome by our present data),30,36 and the third study32 had 186 patients (followed up for at least 24 months), with 73 progressions observed. However, because PFS was limited to small subgroups of patients defined on the basis of site of recurrence, the conclusion of this latter study could be biased and cannot be considered definitive. Although a strength of our study is the number of patients enrolled, which is higher than most studies dealing with the same issue, it is debatable whether the use of several mRNA markers really improves the chances of the RT-PCR technique being a useful detector of CMCs. Indeed, if the postulate that one positive marker is sufficient to diagnose the presence of CMCs were true, then MelanA/MART1, the least sensitive marker, adds little information to TYR and p97, which has a sensitivity of 39% (64 of 163 CMC positive patients), and its evaluation, therefore, could be useless.
Considering sensitivity alone as the measure to choose markers for detecting metastatic tumor cells in peripheral blood can be misleading, which is confirmed by the fact that p97, the most sensitive marker in our series of patients (82%), has been demonstrated to be among the least specific markers for melanoma cells. Indeed, we found that p97 was detected in the peripheral blood of 19 of 21 (90%) patients with Kaposis sarcoma, whereas in the same patients, MelanA/MART1 and TYR were less frequently detected (occurring in 11 [52%] and three [14%] patients, respectively).41 Therefore, it is important to remember that there is as yet no clear explanation for the presence of p97 mRNA in the blood of normal subjects.42 In addition, our data do not support the hypothesis that any of the markers we tested (ie, p97, TYR, and MelanA/MART1) indicate specific biologically aggressive phenotypes, especially considering that their behavior follows a similar pattern within unadjusted and adjusted analyses. We cannot exclude the possibility that if both the number of positive markers and the probability of developing distant metastases were a function of the number of CMCs, the number of positive markers could be a potentially useful prognostic factor. The linear trend we found when analyzing the risk of progression for patients with positive markers (0, 1, 2, and 3; see Table 3 In conclusion, this study indicates that detection of melanoma-associated mRNA in peripheral blood of melanoma patients at the time of diagnosis by RT-PCR does not add precision to the predictive power of stage of disease. Although it seems reasonable to wait for more mature and definitive results by assessing overall survival in larger series of patients using the same standardized assays and the most specific mRNA markers, such studies should be limited to clinical trials that can help define the prognostic value of RT-PCR detection of CMCs, and they should not be used in clinical practice or affect treatment decision making.
Appendix of other members of the Melanoma Cooperative Group of Naples: Aprea P, Ascierto PA, Bosco L, Botti G, Caracò C, Castello G, Celentano E, Chiofalo MG, Comella G, Daponte A, De Marco MR, Leonardi E, Marfella A, Mazzeo M, Melucci MT, Montella M, Mozzillo N, Napolitano M, Parasole R, Perrone F, Pirozzi G, Satriano SMR, Tatangelo F, National Cancer Institute "G. Pascale," Naples, Italy; Prota G, Satriano RA, Ruocco V, 2nd University of Naples, Italy; Palmieri G, Institute of Genetics of Populations, C.N.R., Alghero (SS), Italy; Cossu A, Lissia A, Tanda F, University of Sassari, Italy.
This article was published ahead of print at www.jco.org. Supported by Italian Ministry of Health, Health Department of Campania Region (Italy), and Regione Autonoma della Sardegna. The Clinical Trials Unit is partially supported by AIRC (Associazione Italiana per la Ricerca sul Cancro). Both G.P. and P.A. contributed equally to this work.
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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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