Reverse transcriptase polymerase chain reaction (RT-PCR) detection of melanoma-related transcripts in the peripheral blood and bone marrow of patients with malignant melanoma. What have we learned?

A new standardized absolute quantitative RT-PCR method for detection of tyrosinase mRNAs in melanoma patients: technical and operative instructions

BACKGROUND

To develop a new absolute quantitative real-time PCR method for blood mRNA tyrosinase assay and to compare this new method with standard RT-PCR nested.

METHODS

Ten blood of melanoma patients (stages I-III), 5 tissue samples, 2 surgical fresh metastatic skin and 3 lymph nodes paraffin-embedded slices were analysed, and 10 negative controls were used. Ten millilitres of blood was analysed for each individual. Three different protocols for RNA extraction and two reverse transcription methods were used. Specific human tyrosinase cDNA fragment was cloned into pcDNA3+ vector and then titrated for the standard curve construction (from 10(6) to 10(1)copies/microl). Recovery assays for RNA and cells were also performed.

RESULTS

Our method was able to detect less than 5 cells/10(8) WBC and about 100 fg of tyrosinase RNA. Very low CVs (<1.5%) were obtained on all samples run in triplicate. Sensitivity and specificity were of 100%. The amount of starting volume of blood was crucial for the determination of copy number since large volumes are necessary for patient's monitoring.

CONCLUSIONS

Our absolute qRT-PCR assay could be proposed as a new standardized molecular method for the management of melanoma patients, particularly for the follow up of the highest AJCC stages.

Prognostic role of circulating melanoma cells detected by reverse transcriptase-polymerase chain reaction for tyrosinase mRNA in patients with melanoma

A need for factors predictive of prognosis is present in patients who are diagnosed with malignant melanoma. The detection of circulating melanoma cells by reverse transcriptase-polymerase chain reaction for tyrosinase mRNA is a possible negative prognostic factor. The aim of this study was to assess the prognostic value of reverse transcriptase-PCR for tyrosinase mRNA in peripheral blood samples. From January 2000 to February 2003, duplicate blood samples were drawn from 114 melanoma patients following surgery and informed consent, and were tested with reverse transcriptase-PCR, for tyrosinase mRNA. Outer primers for the first PCR were R1 (sense): TTGGCAGATTGTCTGTAGCC and R2 (antisense): AGGCATTGTGCATGCTGCT. For the second round of PCR, nested primers were R3 (sense): GTCTTTATGCAATGGAACGC and R4 (antisense): GCTATCCCAGTAAGTGGACT. Threshold for detection of the technique was determined by adding serially diluted MelJuSo cells to healthy volunteer blood samples. Overall, 91 (79.1%) patients tested negative for tyrosinase mRNA and 24 (20.9%) tested positive. The number of patients who tested positive by stage was 3/38 (7.9%) for stage I, 3/22 (13.6%) for stage II, 5/30 (16.7%) for stage III and 13/24 (54.2%) for stage IV (P< 0.0001). 11/90 (12.2%) patients with no evidence of disease (stage I, II and III) tested positive and 13/24 (54.2%) patients with clinically confirmed distant metastases (stage IV) tested positive (P<0.00001). With median follow-up of 372 days or to death (range: 0-1303 days), median progression-free survival has not been reached for tyrosinase-negative patients and was 265 days for tyrosinase-positive patients (P<0.00001, log-rank test=21.07). Median overall survival was 344 days for tyrosinase-positive patients and has not been reached for tyrosinase-negative patients (P=0.0001, log-rank test=21.38). Stage, Breslow thickness and result of RT-PCR were significant prognostic factors for disease-free survival in a multivariate analysis, and stage was the only significant prognostic factor for overall survival. In conclusion, detection of circulating melanoma cells by reverse transcriptase-PCR for tyrosinase mRNA is a significant adverse prognostic factor for disease-free survival in patients with malignant melanoma.

Melanoma-reactive T cells in the bone marrow of melanoma patients: association with disease stage and disease duration

Using IFN-gamma enzyme-linked immunospot, we investigated reactivity of T cells from bone marrow and peripheral blood to melanoma lysate-pulsed autologous dendritic cells in 40 melanoma patients. Melanoma-reactive T cells were present in the bone marrow of seven patients and in peripheral blood of four patients. In the bone marrow, melanoma-reactive T cells were present in 6 of 21 stage IV patients and in 1 of 10 stage III patients, whereas none were detected in stage I to II patients (0 of 9). The occurrence of tumor-reactive bone marrow T cells in melanoma patients was associated with advanced disease stage, disease duration and tumor load, and independent of treatment. These findings provide new insights into the generation of T-cell responses in melanoma patients.

Molecular Staging in Stage II and III Melanoma Patients and Its Effect on Long-Term Survival

Purpose

To assess the prognostic value of serial reverse transcriptase polymerase chain reaction (RT-PCR) -based measurements of tyrosinase mRNA in peripheral blood of stage II and III melanoma patients.

Patients and Methods

During routine follow-up of American Joint Committee on Cancer stage II and III melanoma patients, serial testing for tyrosinase transcripts in peripheral blood was performed by RT-PCR. The PCR results were compared with the clinical data collected during the follow-up.

Results

Over a period of 3 years, 111 patients (78 stage II and 33 stage III patients) were enrolled, and tyrosinase determinations were carried out. The 6-year disease-specific survival probability was 97% for patients always showing negative RT-PCR results and 67% for patients who tested positive at least once. In a Cox proportional hazards model, the prognostic value of sex, age, site of primary tumor, histologic subtype, stage, Breslow's tumor thickness, Clark level, and the time-dependent variable PCR result was assessed. Patients with a positive RT-PCR test had a distinctly higher risk of dying from melanoma, with a hazard ratio of 12.6 (95% CI, 3.4 to 46.3; P < .001).

Conclusion

Our study shows a strong association between PCR and disease-specific survival time. Detection of tyrosinase mRNA in peripheral blood may be of similar importance for the clinical course of melanoma as the detection of micrometastatic disease in the sentinel lymph node. Whether a combination of these two factors leads to a better definition of the prognosis of melanoma patients is under investigation in current studies.

Quantification of melanoma mRNA markers in sentinel nodes: pre-clinical evaluation of a single-step real-time reverse transcriptase-polymerase chain reaction assay

Although reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of melanocyte-associated mRNA can detect sentinel node melanoma metastases, most published assays are semi-quantitative methods of unknown sensitivity and precision, unsuitable for clinical use. We describe a single-step real-time quantitative RT-PCR assay for MART-1 and tyrosinase mRNAs, suitable for sentinel node analysis in a clinical setting. Using serial dilutions of melanoma cell line SK-MEL-28 RNA in water as a calibrator, we obtained linear calibration curves covering the range 0.5 to 10,000 arbitrary units (SK-MEL-28 melanoma cell equivalents). The sensitivity limit was 0.32 (MART-1) and 5 (tyrosinase) arbitrary units. Analytical imprecision was between 11% and 34%. MART-1 PCR efficiency was unaffected when samples were diluted with negative lymph node RNA rather than water, whereas tyrosinase PCR efficiency was halved. To evaluate the clinical suitability of our assay, we quantified melanocyte mRNAs in sentinel nodes with histologically verified micrometastases (n = 10) and benign nevus inclusions (n = 10), and in sentinel nodes without evidence of intranodal melanocytes (n = 10). We found significant differences in median melanocyte-derived mRNA levels comparing the three types of lymph nodes, suggesting that this quantitative molecular protocol may increase assay precision and be useful for the clinical evaluation of sentinel nodes.

Molecular detection of circulating tumor cells is an independent prognostic factor in patients with high-risk cutaneous melanoma

Detection of circulating tumor cells (CTCs) might improve current staging procedures by identifying a subgroup of patients with minimal residual disease and thus a higher risk of disease recurrence. Forty patients with > or =2-mm-thick cutaneous melanoma with or without lymph node metastasis were enrolled. After standard radical surgery and adjuvant therapy in case of lymph node metastasis, patients were followed up with routine physical and radiologic assessments as well as serial PCR-based analysis of CTCs using 2 melanoma markers (tyrosinase and Melan-A/Mart-1). After a median follow-up of 30 months, 18 patients had disease recurrence and 28 were PCR-positive before the disease became clinically evident. The sensitivity of the molecular test was 83%. Median time to PCR positivity and median PCR-to-relapse time were 12 and 8 months, respectively. At multivariate analysis, PCR positivity was an independent predictor of disease recurrence (hazard ratio=2.06, 95% CI 1.07-3.35; p=0.03). Among high-risk melanoma patients, serial PCR-based analysis of CTCs can identify a subgroup at higher risk of disease recurrence, with clinically significant advance. Therefore, CTC detection might be employed for the selection of patients for adjuvant treatment and during follow-up for early indication of therapeutic failure.

The history and future of melanoma staging

The evolution and progressive refinement of an internationally accepted melanoma staging system over the last 50 years has resulted in much greater accuracy and increased utility, but the staging process has become more complex and less intuitive. This raises the question of whether melanoma staging should continue to develop with ever-increasing levels of complexity, or whether attempts should be made to produce an alternative system that is simpler and more intuitive. The current, TNM-based American Joint Committee on Cancer (AJCC) staging system for melanoma incorporates only some of the prognostic factors of proven significance. However, the information that is now available about these and other, well-documented prognostic factors allows accurate prediction of an individual melanoma patient's prognosis using a computer-generated estimate. Thus an alternative staging strategy that could be considered in the future would be to use such an estimate to obtain a numerical score for each patient, based on all available information agreed to be of prognostic relevance. A stage grouping could then be assigned on the basis of that score, according to previously determined score ranges for each stage and substage. The advantages of such a system would be that it would allow more reliable comparison of treatment results within and between institutions, and would provide more equivalent stratification groups for patients entering clinical trials of new therapies and those entering adjuvant therapy trials. A further advantage would be that because there would be a direct link between staging and prognostic estimate, such a system would be more readily able to be understood in an intuitive fashion.

Dermatoscopic and histopathological diagnosis of primary and metastatic melanoma: report of a workshop at the Third Research Meeting on Melanoma, Milan, Italy, May 2003

The clinical and histopathological session of the Third Research Meeting on Melanoma, Milan, Italy, held in May 2003, highlighted several key topics, including clinical, dermatoscopic and computer-aided diagnosis and the use of immunohistochemical, immunological and biochemical approaches to diagnosis and monitoring. This report is a brief summary of the main themes covered.

Detection of micrometastases in sentinel lymph nodes from melanoma patients

The technique of sentinel lymph node (SLN) dissection is a reliable predictor of metastatic disease in the lymphatic basin draining the primary melanoma. Reverse transcription-polymerase chain reaction (RT-PCR) is emerging as a highly sensitive technique to detect micrometastases in SLNs, but its specificity has been questioned. A prospective SLN study in melanoma patients was undertaken to compare in detail immunopathological versus molecular detection methods. Sentinel lymphadenectomy was performed on 57 patients, with a total of 71 SLNs analysed. SLNs were cut in slices, which were alternatively subjected to parallel multimarker analysis by microscopy (haematoxylin and eosin and immunohistochemistry for HMB-45, S100, tyrosinase and Melan-A/MART-1) and RT-PCR (for tyrosinase and Melan-A/MART-1). Metastases were detected by both methods in 23% of the SLNs (28% of the patients). The combined use of Melan-A/MART-1 and tyrosinase amplification increased the sensitivity of PCR detection of microscopically proven micrometastases. Of the 55 immunopathologically negative SLNs, 25 were found to be positive on RT-PCR. Notably, eight of these SLNs contained naevi, all of which were positive for tyrosinase and/or Melan-A/MART-1, as detected at both mRNA and protein level. The remaining 41% of the SLNs were negative on both immunohistochemistry and RT-PCR. Analysis of a series of adjacent non-SLNs by RT-PCR confirmed the concept of orderly progression of metastasis. Clinical follow-up showed disease recurrence in 12% of the RT-PCR-positive immunopathology-negative SLNs, indicating that even an extensive immunohistochemical analysis may underestimate the presence of micrometastases. However, molecular analyses, albeit more sensitive, need to be further improved in order to attain acceptable specificity before they can be applied diagnostically.

Prognostic value of circulating melanoma cells detected by reverse transcriptase-polymerase chain reaction

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, I-III 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.