New prognostic factors in melanoma: mRNA tumour markers

Old and new serological biomarkers in melanoma: where we are in 2009

Biomarkers play an important role in the diagnosis and prognostic classification of various cancers and can be useful in monitoring the patient's clinical course of disease and response to therapy. Generally, biomarkers are proteins and their expressions are associated with malignant disease. In the majority of cases, the marker molecules are expressed by the tumour cells themselves or by the tumour microenvironment cells. Thus, most biomarkers can primarily be found in malignant tissues, but after active secretion or passive release at tumour destruction, they become detectable in body fluids such as blood. Besides morphological and histopathological biomarkers (anatomic site, type of the primary tumour, tumour size, invasion depth, vascular invasion and ulceration), an increasing variety of serological markers have been identified, providing the possibility of a more detailed diagnostic and prognostic subgrouping of tumour entities, up to and even changing existing classification systems. The goal of this review is to provide an overview of old and more recent serological biomarkers in malignant melanoma. We will first focus on confirmed and nonconfirmed serum tumour markers, followed by proteomic profiling, an innovative approach to identify new and better serological biomarkers in melanoma, and ending with the predictive factors for treatments in this pathology.

Immunomagnetic detection and clinical significance of micrometastatic tumor cells in malignant melanoma patients

PURPOSE

Positive associations between the presence of micrometastatic tumor cells and disease aggressiveness have been reported in several tumor types, but the clinical implications are still not established. We wanted to test a new, sensitive immunomagnetic detection method on bone marrow (BM) and peripheral blood (PB) samples from patients with malignant melanoma and relate the findings to clinical outcome.

EXPERIMENTAL DESIGN

Samples from 210 patients admitted for relapse of cutaneous melanoma were examined. Mononuclear cell fractions isolated from BM and PB were incubated with superparamagnetic particles coated with antimelanoma antibodies. Live tumor cells with bound beads were isolated with a magnet and identified in a microscope as cell-bead rosettes. Beads without antibody or with an irrelevant antibody were used as controls. The whole procedure was completed within 2-3 h. The identity of the cells was confirmed with a new double labeling procedure with fluorescent microparticles.

RESULTS

Rosetted melanoma cells were found in BM aspirates of 35 of 186 (19%) patients, but in only 2 of 208 (1%) PB samples. The controls were all negative. After a median observation time of 1.1 year (range, 0-6.8 years), patients with tumor cells in BM showed a significantly shorter overall survival from time of BM aspiration (P = 0.009). In multiple regression analysis, a positive BM test was a strong indicator of overall survival (P = 0.021), associated with disease stage (American Joint Committee on Cancer) and with the number of metastatic sites, but not with the primary (Breslow) tumor depth and morphology.

CONCLUSIONS

The results demonstrate the prognostic significance of detecting BM micrometastasis in melanoma patients. The results strengthen the validity of the immunobead technique. In contrast to other techniques, the method identifies intact, live tumor cells that can be further characterized, making the assay attractive for extended use.

High frequency of melanoma-associated antigen or HLA class I loss does not correlate with survival in primary melanoma

Melanoma-associated antigens are at the center of many immunotherapeutic trials in melanoma. Little is known about the impact of antigen expression on the natural course of disease. We stained 110 cases of primary melanoma with a median follow-up of 13 years (range 10-18 years) for melanoma-associated antigens gp100, MelanA/MART-1, MAGE-3, tyrosinase, and for HLA class I molecules. Of 91 cases evaluated, we found immunoreactivity for gp100, MelanA/MART-1, and tyrosinase in 88%, 80%, and 87% of primary tumors, respectively, for MAGE-3 in 37% and for HLA class I in 86% of primary tumors. Loss, that is, heterogeneous expression within primary tumors, was most pronounced for gp100 (73% of primary tumors) and least for MAGE-3 (27% of primary tumors). MelanA/MART-1 and tyrosinase expression loss was 58% and 59% of primary tumors, respectively. There was a high rate of expression loss for HLA class I (74%). Univariate and multivariate statistical analysis of expression in primary tumors and loss of melanoma antigens as well as HLA class I in individual primary tumors showed no significant correlation to overall survival. Loss of gp100 and loss of tyrosinase expression showed a negative survival trend over homogeneous expression of these antigens, although not reaching statistical significance (P = 0.08 and P = 0.09, respectively). We conclude that loss of melanoma antigen expression as well as HLA class I expression is a frequent observation in primary melanoma. However, no statistically significant correlation between loss of these antigens in individual primary tumors and negative impact on overall survival was found in our cohort.

Melanoma patient staging: histopathological versus molecular evaluation of the sentinel node

Lymphatic mapping and sentinel lymphadenectomy provide a minimally invasive means of directly determining the status of the regional lymph nodes in all patients who have a primary melanoma >1 mm thick but no clinical evidence of nodal involvement. Since the histological status of the sentinel node (SN) has been shown to be the most important prognostic factor in primary melanoma patients, the World Health Organization has recently recommended that sentinel lymphadenectomy should become the new standard of care for primary melanoma patients. This paper reviews the literature with regards to developments in and the current status of SN evaluation. Developments in the histopathological versus molecular detection of melanoma nodal metastases are reviewed, with specific emphasis on the strengths, limitations and clinical significance of these techniques. Molecular evaluation of the SN offers several advantages over standard histopathological analysis. These include an improved sensitivity, the cost-effective use of multiple markers for the improvement of detection rate and prognosis, as well as being less labour-intensive and costly. Moreover, molecular analysis has the potential to allow estimation of tumour burden. We review the potential causes of technical false-negative and false-positive reverse transcription-polymerase chain reaction (RT-PCR) results and how these could be eliminated by a systematic approach consisting of (i) careful and systematic assay design, which would include efficient tissue homogenization, choice of reagents and molecular markers, primer design and the use of one-stage versus two-stage PCR; (ii) careful optimization of the RT-PCR parameters (in particular the PCR cycle number) through the use of appropriate control tissues; and (iii) aiming for high assay reproducibility and lastly by applying the necessary positive and negative controls with each batch of samples. We also review the significant improvement in patient prognosis and management that has been made possible by the development of sentinel lymphadenectomy and histopathological evaluation of the SN, and compare the clinical (predictive) value of histopathological analysis with that of RT-PCR. Although RT-PCR is able to detect additional, clinically significant SN metastases that are missed by routine histopathology, its current limitation is that it overestimates the number of patients who have clinically significant melanoma metastases. Therefore, we suggest and discuss appropriate steps that need to be taken in order to minimize these false-positives and make this molecular tool more acceptable for routine clinical use.

Evaluation of standard tyrosinase RT-PCR in melanoma patients by the use of the LightCycler system

BACKGROUND

Haematogenous spread influences outcome in melanoma patients. The clinical relevance of detecting circulating melanoma cells in peripheral blood by tyrosinase mRNA RT-PCR is, however, questioned as rates of positivity considerably vary between studies. Standard tyrosinase-nested RT-PCR was here compared with a real-time PCR technique.

METHODS

Forty-three blood samples from 20 stage III--IV melanoma patients were analyzed. Mononuclear cells were isolated using a Ficoll Hypaque gradient technique. Total RNA extracted by the acid guanidinum thiocyanate-phenol-chloroform method was reverse transcribed using random hexamers or specific primers. Standard tyrosinase-nested PCR was performed on Touchdown machine (Hybaid) and real-time PCR on a LightCycler instrument (Roche).

RESULTS

Only two samples from stage IV patients (one from random hexamers, one from antisense primers) were found tyrosinase positive with a 100% agreement between the two PCR techniques. A 10-fold dilution of the first-round products improved the PCR kinetic and the final amount of amplified product of positive samples, but not the rate of positivity.

CONCLUSIONS

Efficiency of the PCR reaction can be monitored in an online fashion by the LightCycler instrument allowing technical improvements. However, tyrosinase mRNA RT-PCR cannot be yet considered as a useful technique in the monitoring of melanoma patients.

Detection of occult melanoma cells in paraffin-embedded histologically negative sentinel lymph nodes using a reverse transcriptase polymerase chain reaction assay

PURPOSE

Detection of occult metastasis before the development of clinical disease could allow more accurate staging, appropriate follow-up procedures, and adjuvant therapies in patients with malignant melanoma (MM). The sentinel lymph node (SLN) has been proposed as a reliable predictor of metastatic disease in the lymphatic basin draining the primary melanoma. In this study, we screened both paraffin-embedded SLNs and peripheral-blood (PB) samples from MM patients at various stage of disease using a multimarker reverse transcriptase polymerase chain reaction (RT-PCR) assay. The prognostic significance of the presence of PCR-positive markers was also evaluated.

PATIENTS AND METHODS

Total RNA was obtained from paraffin-embedded SLN sections and PB samples of 75 MM patients. RT-PCR was performed using tyrosinase and MelanA/MART1 as melanoma-associated markers. Radiolabeled PCR products were analyzed on denaturing polyacrylamide gels.

RESULTS

Good sensitivity of the RT-PCR assay on archival tissues was demonstrated after comparison of RT-PCR results on frozen and paraffin-embedded SLNs from 16 MM patients. Significant correlation between the disease stage and marker expression in both PB and SLN samples was observed; the highest value was for patients who were positive for both markers in SLN (P =.006). Progression of disease was significantly associated with the total number of PCR-positive markers in both PB (P =.034) and SLN (P =.001) samples.

CONCLUSION

Although sensitivity is lowered by the use of paraffin-embedded specimens, our data indicate that RT-PCR analysis of serial sections from archival SLNs may be helpful in improving detection of occult micrometastases, thus improving staging of patients with melanoma.

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?

The detection of circulating tumor cells (CTC) and bone marrow micrometastases (BMM) by reverse transcriptase polymerase chain reaction (RT-PCR) may help predict recurrence and survival in malignant melanoma (MM). Since the appearance of the original article by Smith et al. in 1991 (Lancet 338:1227), several groups have attempted the detection of CTC and BMM in MM using RT-PCR for melanocytic specific markers, mainly tyrosinase mRNA. Most studies show that tyrosinase is not present in the PB and BM of control individuals without MM. The PCR positivity rates in MM are extremely variable, ranging from 0% to 100%. There was a correlation between RT-PCR and stage in some but not all of the studies. These disparate findings could in part be explained by differences in RNA extraction and blood separation techniques, to unrecognized contamination leading to false positive results, or differences in patient selection. Despite these discrepancies, we and others have shown that RT-PCR for tyrosinase mRNA in PB is able to predict overall survival (OS) and disease-free survival (DFS) in a statistically significant manner. In AJCC stage II-IV patients rendered surgically free of disease, we found that blood tyrosinase positivity was an independent predictor of OS and DFS. We also found that BM tyrosinase positivity is an independent predictor of DFS in the same group of patients. RT-PCR may help identify subgroups of patients at high risk for early relapse for more aggressive adjuvant therapy. Large prospective studies and interlaboratory quality assurance initiatives are necessary to confirm the accuracy and prognostic value of these RT-PCR assays.

Surgical treatment of neuroblastoma with micrometastasis

BACKGROUND/PURPOSE

The aim of this study was to define the role of surgery in neuroblastoma with micrometastasis, which is detectable only by the polymerase chain reaction (PCR) method.

METHODS

Fifty samples (peripheral blood 9, bone marrow 41) were harvested sequentially from 27 neuroblastoma patients, and the micrometastases were examined using the previously described single-step PCR method. The results were reviewed with the clinical courses.

RESULTS

Radical surgery was performed in 9 patients with bone marrow micrometastasis. Event-free survival was obtained in 2 patients with stage IV disease (25.0%) for a follow-up period of 2 to 6 years in this group. Both patients received intraoperative radiation and subsequent autologous bone marrow transplantation (ABMT) using purged marrow. Radical surgery was performed in 18 patients without micrometastasis, and 6 of 9 advanced patients (66.7%) survived without the disease including 4 patients who received unpurged stem cell transplantation.

CONCLUSIONS

Persistent micrometastasis in bone marrow should be considered predictive as a poor prognostic factor in neuroblastoma. Intensive local control with surgery and radiation is important for the patients with micrometastasis and should be followed by ABMT using purged marrow. Unpurged marrow may be safely used if the single-step PCR detects no micrometastasis.

Detection of circulating breast cancer cells by reverse transcriptase polymerase chain reaction (RT-PCR)

The confounding problem in treatment of breast cancer is the metastasis of breast tumour. Reverse transcriptase polymerase chain reaction (RT-PCR) has been recently used in the detection of circulating breast cancer cells. This review reports on the development of this assay as well as its advantages and disadvantages. We feel that cytokeratin 20 and beta -human chorionic gonadotropin (hCG) mRNA are the best markers for the detection of circulating breast cancer cells. We suggest that the multiple RNA marker RT-PCR assay can help to increase both sensitivity and specificity of detection, and that quantitative RT-PCR assay is more effective than the qualitative assay in the detection of circulating breast cancer cells.

Serological markers for melanoma

We present a review of current literature concerning the significance of serological markers in melanoma patients. Results for cytokines, cytokine receptors, cell adhesion molecules, S100 protein, melanoma inhibitory activity, tissue-specific reverse transcription-polymerase chain reaction, neurone-specific enolase, lipid-bound sialic acid and melanin metabolites such as 5-S-cysteinyldopa and 6-hydroxy-5-methoxyindole-2-carboxylic acid are discussed. For most of these substances, serum levels are more pronounced in the more advanced stages of disease. Therefore, these markers seem to have no place in the early detection of melanoma. On the other hand, sensitivity in the advanced stages of disease seems to be < 100%, compromising their use as a new staging procedure. Some markers show promising results as a possible prognostic factor in the early detection of disease progression or in the prediction of therapy outcome. If confirmed by further studies, this could direct future therapeutic strategies and could help to select patients who would benefit most from more aggressive (adjuvant) therapies. In addition, the study of some of these substances could add to the knowledge of tumour biology and immunology.

Molecular and prognostic classification of advanced melanoma: a multi-marker microcontamination assay of peripheral blood stem cells

The presence or absence of melanoma cells in human peripheral blood has recently been shown to be associated with disease prognosis, including overall survival. The detection of tyrosinase mRNA-positive circulating melanoma cells by reverse transcription-polymerase chain reaction (RT-PCR) has been limited to disseminated tumours expressing measurable amounts of this melanocyte-specific enzyme. To biologically classify both melanotic and amelanotic melanomas and to evaluate the clinical and prognostic relevance of tumour cell microcontamination, we examined autologous peripheral blood stem cell (PBSC) harvests from patients with advanced malignant melanoma prior to dose-escalated chemotherapy. To assay heterogeneous melanoma cell antigen expression, we developed a highly sensitive RT-PCR using four melanoma- and one tumour-associated antigen as molecular markers. Expression of the melanocyte-associated transcripts of tyrosinase, MART1/Melan-A, tyrosinase-related protein-1 (TRP-1) and tyrosinase-related protein-2 (TRP-2) as well as the tumour-specific transcript of MAGE-3 was analysed by RT-PCR in PBSC harvests from 31 patients. Seven of the 31 PBSC harvests tested positive for one or more molecular markers: two patients for tyrosinase only, and one patient for MAGE-3 only, one patient for tyrosinase and MAGE-3, one for tyrosinase and MART1/Melan-A, and two patients for tyrosinase, MART1/Melan-A, TRP-2 and MAGE-3. mRNA-positive patients exhibited a significantly impaired overall survival (P = 0.0032), with a median survival of 3 months as opposed to 10 months in PBSC mRNA-negative patients. In conclusion, the use of this multiple-marker microcontamination assay allowed for molecular and prognostic classification of advanced malignant melanoma.

Molecular detection and characterisation of circulating tumour cells and micrometastases in solid tumours

The detection and molecular characterisation of circulating tumour cells (CTC) and micrometastases may have important prognostic and therapeutic implications. Because their numbers are very small, these tumour cells are not easily detected using conventional methods. In the last decade, numerous groups have attempted to detect occult tumour cells in solid malignancies using the highly sensitive reverse transcriptase polymerase chain reaction (RT-PCR). These assays were in the vast majority directed against tissue-specific markers. PCR was shown to be superior to conventional techniques in detecting occult tumour cells allowing the identification of one malignant cell mixed with 1-10 million normal cells. In some tumours like melanoma and prostatic carcinoma, tissue-specific transcripts were detected with high specificity in the blood of patients with localised and advanced disease. In some reports, PCR was shown to be a strong predictor of poorer outcome. However, due to the many limitations of PCR (e.g false-positives), many groups are developing new approaches for the detection of occult tumour cells. The most attractive technique involves immunomagnetic isolation of CTC and micrometastases prior to downstream analysis. The tumour-rich magnetic fraction can be subjected to RT-PCR, immunocytochemistry and in situ hybridisation. This will lead to better quantification and molecular characterisation of these tumour cells. In conclusion, the molecular detection and characterisation of occult tumour cells offer a great opportunity for better stratifying patients with solid tumours and for developing new prognostic markers and targeted therapies.

Detection and clinical relevance of micrometastatic cancer cells

The failure to reduce mortality of epithelial cancer patients is probably a result of the early dissemination of cancer cells to secondary sites, which is usually missed by conventional diagnostic procedures used for tumor staging. Individual carcinoma cells present in regional lymph nodes, blood, or distant organs (eg, bone marrow) can be detected by sensitive immunologic or molecular methods. Because the goal of adjuvant therapy is the eradication of occult micrometastatic tumor cells before metastatic disease becomes clinically evident, the early detection of micrometastases could identify those patients who might benefit from adjuvant therapy. In addition, more sensitive methods for detecting such cells should increase knowledge about the biologic mechanisms of metastasis, which might improve the diagnosis and treatment of micrometastatic disease. In this article, the recent developments in sensitive assays used for the detection of individual micrometastatic cancer cells in patients with epithelial tumors are reviewed.