The detection of tyrosinase-specific mRNA in bone marrow is not more sensitive than in blood for the demonstration of micrometastatic melanoma

The role of molecular staging in malignant melanoma

AIMS

To review the role of tyrosinase RT-PCR in the detection of clinically occult metastatic disease, both within the regional lymph nodes and peripheral blood of patients with malignant melanoma. Secondly, to assess whether the detection of such minimal disease has clinical implications for patients with melanoma.

METHODS

A review of the literature was undertaken by searching the MEDLINE database for the period 1966-2002 without any language restrictions. Keywords included 'Molecular staging of melanoma', 'Reverse transcription polymerase chain reaction', 'Malignant melanoma' and 'Tyrosinase'.

CONCLUSIONS

Detection of tyrosinase RT-PCR positive cells within the peripheral blood correlates with the clinical stage of malignant melanoma, the primary tumour thickness and other known prognostic indicators. Positive tyrosinase RT-PCR is associated with a reduction of disease-free survival and overall survival. Current studies demonstrate a higher rate of recurrence in RT-PCR positive patients with clinical stage II and III disease. Implications of a positive result within the regional lymph nodes are less well defined. A significant correlation has been demonstrated between positive results and increasing primary melanoma thickness. However, a large number of false-positive results have been demonstrated, due to benign naevi and schwann cells, which may hamper any statistically significant conclusions being reached.

Prognostic value of tyrosinase reverse-transcriptase polymerase chain reaction in metastatic melanoma

BACKGROUND

Circulating tumor cells can now be identified in subjects with metastatic melanoma by using the reverse-transcriptase polymerase chain reaction (RT-PCR) to detect the messenger RNA of tyrosinase, a key enzyme of melanogenesis.

AIM AND METHODS

The aim of this study was to determine whether the detection of positive tyrosinase cells in patients at metastatic stage was associated with a worse evolution. 32 patients were included with metastatic melanoma (AJCC IV).

RESULTS

66% had a positive tyrosinase RT-PCR and a shorter survival compared with patients with a negative RT-PCR, but this difference is not statistically significant. However, a positive test could appear indicative of rapid progression and poor prognosis.

CONCLUSION

The prognostic value of this method could be improved by combining it with PCR of other melanoma markers (Melan A, Mage 3) or assays of serum markers (S 100 protein or lactate dehydrogenase).

Detection of melanoma cells in sentinel lymph nodes, bone marrow and peripheral blood by a reverse transcription-polymerase chain reaction assay in patients with primary cutaneous melanoma: association with Breslow's tumour thickness

BACKGROUND

Tyrosinase reverse transcription-polymerase chain reaction (RT-PCR) has been shown to be highly sensitive in detecting tumour cells in melanoma patients.

OBJECTIVE

To assess whether the detection of minimal residual disease by RT-PCR is improved by concomitant analysis of sentinel lymph nodes (SLNs), bone marrow (BM) and peripheral blood (PB) in patients with primary melanoma.

METHODS

Thirty-five SLNs, 41 BM samples and 26 PB specimens from 26 patients with primary cutaneous melanoma (tumour thickness > or = 0.75 mm) were examined by nested RT-PCR for tyrosinase and Melan-A. SLNs and BM samples were also analysed by histopathology. RT-PCR findings were related to tumour thickness of the primary melanoma.

RESULTS

Overall, melanoma cells were detected by RT-PCR in 13 of 26 patients (50%). Seven patients had positive RT-PCR results in their SLNs (27%), including all patients (n = 4) with histologically positive SLNs, two patients had positive findings in their BM exclusively detected by RT-PCR (8%) and six patients in PB (23%). The presence of tumour cells detected by RT-PCR in SLNs was not related to the presence of melanoma cells in BM and/or PB. The incidence of RT-PCR-positive SLNs was significantly associated with greater tumour thickness (P = 0.004). Both patients with positive RT-PCR findings in their BM had a large tumour thickness (> or = 2 mm). No association between positive RT-PCR findings in PB and greater tumour thickness was observed.

CONCLUSIONS

RT-PCR-positive SLNs were strongly associated with greater tumour thickness, underlining the prognostic significance of SLN positivity. Similar to certain epithelial malignancies, molecular investigation of the BM might provide complementary prognostic information in the early stages of melanoma. In contrast, no association between positive RT-PCR results in PB and increasing tumour thickness was found, implying that RT-PCR findings in PB are of doubtful clinical relevance in primary melanoma.

Immunobead-based detection and characterization of circulating tumor cells in melanoma patients

The presence of circulating tumor cells in bone marrow and peripheral blood of cancer patients may reflect the aggressiveness of the disease. This also applies to cancers that rarely give rise to overt bone marrow metastases. The clinical validity of micrometastasis detection for staging and prognostication depends on the sensitivity and reliability of the detection method. In malignant melanoma, most studies have used reverse transcriptase polymerase chain reaction (RT-PCR) techniques, commonly with tyrosinase mRNA as the target molecule. Unfortunately, highly inconsistent results have been reported, raising doubts about this approach. In a study of 81 melanoma patients with metastatic disease, we used an immunobead rosetting method in which live melanoma cells are selected and identified by binding of paramagnetic beads coated with the 9.2.27 antibody against the high molecular weight melanoma-associated antigen. In bone marrow samples obtained from 60 patients, 14 (23.3%) were positive, compared to only two of 81 in blood. A highly significant correlation (p = 0.0001, log rank test) was found between micrometastasis positivity and overall survival from time of removal of the primary tumor. Moreover, in regression analysis it was found that the presence of micrometastatic cells was an independent and the most important indicator of poor prognosis, with a relative risk of 5.38. The immunomagnetic method is simple, rapid, and highly sensitive and will be used in further prospective clinical studies.

Polymerase chain reaction in the detection of circulating tumour cells in peripheral blood of melanoma patients

Conflicting results were obtained by various research groups using the tyrosinase reverse transcription polymerase chain reaction (RT-PCR) for detecting melanoma cells circulating in peripheral blood. Whereas 100% positivity was initially reported for stage IV patients, more recent investigations reported positive detection rates between 30% and 50% in patients with disseminated melanoma. While the high detection rate initially reported in metastatic melanoma may be explained by contamination problems, methodological differences in different steps of the technical procedure of RT-PCR may account for the differences reported in more recent examinations. Major differences may result from the kind of blood preparation, the RNA isolation method, the kind of RT enzyme used, and the gene targeted by PCR primers. In our experience, blood purification by a Ficoll gradient increased melanoma cell detection rates compared to RNA extraction from total blood or after erythrocyte lysis. Amplification of MelanA in addition to tyrosinase resulted in a 30% enhanced sensitivity of melanoma cell detection compared to amplification to tyrosinase alone, whereas gp100/pMel17 and MUC18 gene products were already detected in blood from nonmelanoma patients. These findings are in agreement with those of other groups. Currently, an increase in the sensitivity for detection of circulating tumour cells to more than 50% of patients with disseminated melanoma seems to be unlikely. It is interesting that between 15% and 30% positive results and sometimes more have already been obtained from patients with primary melanoma. So far, there is no data for judging the prognostic significance of the detection of circulating tumour cells in patients without clinically recognisable metastases. Our limited experience shows that staging examinations in these patients reveal no proof of macrometastasis. Therefore, it is presently unclear whether these positive findings are associated with long-term prognosis or if they merely reflect false positive findings in this highly sensitive RT-PCR technique.

Prognosis of metastatic melanoma: no correlation of tyrosinase mRNA in bone marrow and survival time

Recent publications suggest that tyrosinase mRNA in blood as well as in bone marrow is detectable only in a subgroup of patients with metastatic melanoma. This would imply that tyrosinase mRNA is of limited value as a tumor marker. We addressed the question of whether patients with metastatic melanoma and RT-PCR-detectable tyrosinase mRNA in blood or bone marrow have a different prognosis than tyrosinase mRNA-negative patients. Twenty melanoma patients with widespread clinical metastases were enrolled; the survival time after first diagnosis of visceral metastases was correlated to tyrosinase mRNA presence in blood and bone marrow samples. The time of survival of eight patients with metastatic melanoma and detectable tyrosinase mRNA in either blood or bone marrow was not different from the prognosis of 12 patients without detectable tyrosinase mRNA in either blood or bone marrow. Detection of tyrosinase mRNA in blood or bone marrow samples of melanoma patients with advanced disease seems to have no substantial relevance for survival time and outcome of disease. In this constellation, detection of tyrosinase mRNA by RT-PCR is not a valid tumor marker. Nevertheless, tyrosinase positivity in bone marrow in earlier tumor stages might indicate increased risk for the development of distant metastases. This should be addressed in further studies.

No correlation of tyrosinase mRNA in bone marrow with prognosis of metastatic melanoma

BACKGROUND

Recent publications suggest that tyrosinase mRNA in blood as well as in bone marrow is detectable only in a subgroup of patients with metastatic melanoma.

OBJECTIVE

We addressed the question, whether patients with metastatic melanoma and with RT-PCR-detectable tyrosinase mRNA in blood or bone marrow have a different prognosis compared to tyrosinase mRNA-negative patients.

METHODS

20 melanoma patients with widespread clinical metastases were enrolled and the survival time after first diagnosis of visceral metastases was correlated to tyrosinase mRNA presence in blood and bone marrow samples.

RESULTS

The time of survival of 8 patients with metastatic melanoma and detectable tyrosinase mRNA in either blood or bone marrow was not different from the prognosis of 12 patients without detectable tyrosinase mRNA in either blood or bone marrow.

CONCLUSION

Although based on a limited number of patients our results suggest that detection of tyrosinase mRNA in blood or bone marrow samples of melanoma patients with advanced disease seems to have no substantial relevance for survival time and outcome of disease. For this purpose, detection of tyrosinase mRNA by RT-PCR is not a valid tumor marker. Nevertheless, tyrosinase positivity in bone marrow in earlier tumor stages might indicate increased risk for the development of distant metastases. This should be addressed in further studies.

Molecular detection of low-level disease in patients with cancer

The accurate detection of low-level disease in patients with cancer is essential to improve the staging of disease and consequently to define appropriate treatment strategies. Most methods currently used for staging are based on imaging studies and histological and immunocytochemical analysis of tissues such as bone marrow aspirates, or antibody assays for marker proteins secreted into the circulation. These methods have limited sensitivity. However, assays for nucleic acid-based markers may be valuable tools for the sensitive detection, assessment, and monitoring of disease status in asymptomatic cancer patients. Application of these methods may allow the early detection of cancer, when the tumour burden is smaller and the disease potentially more curable. The last decade has seen the application of polymerase chain reaction (PCR)-based methods to the detection of tumour in a wide variety of compartments, including peripheral blood, bone marrow, lymph nodes, urine, sputum, faeces, pancreatic juice, and more recently plasma. Molecular detection of disease by PCR has targeted DNA and RNA markers, including mutations, microsatellites, and tissue-specific gene expression. It is likely that these molecular methods will provide important clinical information, though their current clinical utility remains unclear. The current status of nucleic acid-based assays for the detection and assessment of disease status in the management of patients with solid tumours is reviewed.