Specificity of tyrosinase and HMB45 PCR in the detection of melanoma metastases in sentinel lymph node biopsies

New Developments in the Staging of Melanoma

As the incidence of melanoma increases, so does the search for new staging techniques that may provide important prognostic information and aid in the detection of early metastatic disease. The application of molecular techniques may provide powerful new tools in this search. This review summarizes recent findings obtained by means of conventional RT-PCR, cDNA arrays, and proteomics in the investigation of human melanoma. The molecular tools discussed in this review demonstrate how global transcript and protein analysis might contribute not only to the staging of melanoma, but may hold great promise in improving the diagnosis and treatment of this disease.

Prognostic value of tyrosinase reverse transcriptase PCR analysis in melanoma sentinel lymph nodes: long-term follow-up analysis

OBJECTIVE

To determine the prognostic value of detecting tyrosinase transcripts in melanoma sentinel lymph nodes (SLNs).

METHODS

Reverse transcription (RT) PCR for tyrosinase mRNA was performed on negative SLNs of 76 patients with melanoma.

RESULTS

Tyrosinase mRNA was found in 39 patients (51.3%). After a median follow-up period of 51 months, significant differences were found in overall survival (OS) but not in disease-free survival (DFS). The 5-year OS and DFS rates were 97.2% and 80%, respectively, for RT-PCR tyrosinase-negative (TN) patients vs. 78.67% and 66.24% for RT-PCR tyrosinase-positive (TP) patients (P = 0.019 and P = 0.38, respectively). Of four progressing patients in the TN group, three relapsed with subcutaneous, soft-tissue or lymph-node metastases, while seven out of nine progressing patients in the TP group relapsed at visceral sites.

CONCLUSIONS

No significant differences in DFS were found by RT-PCR tyrosinase expression analysis at melanoma SLNs. Significant differences in OS could be related to a different pattern of relapse and must be confirmed after a longer follow-up time.

Serological reagents for the immunohistochemical analysis of melanoma metastases in sentinel lymph nodes

For the immunohistochemical analysis of melanoma, various serological reagents are available. Melanocyte differentiation markers are reactive with cells and tumors of melanocytic lineage. HMB45 to gp100 has been the most commonly used melanocyte differentiation marker. Recently it was complemented by reagents such as antibodies to Melan-A/MART-1 and tyrosinase. Other reagents, whose reactivity is not strictly confined to melanocyte differentiation antigens, are also commonly used. Among them, the most prominent is S100. Other reagents are D5 to MITF or PNL-2. The properties of these reagents are presented, and their usefulness as markers in the setting of metastatic melanoma in sentinel lymph nodes is discussed.

False-positive cells in sentinel lymph nodes

Melanoma sentinel lymph nodes (SLN) are carefully evaluated to maximize sensitivity. Examination includes hematoxylin and eosin (H+E) stained sections at multiple levels through the node, with subsequent immunohistochemical (IHC) stains for melanocytic markers if H+E sections are negative for melanoma. However, not all IHC-positive cells in SLN are metastatic melanoma, as evidenced by the presence of MART-1 positive cells in SLN from breast cancer patients with no history of melanoma (so-called 'false-positive' cells). These 'false-positive cells' could be nodal nevus, non-melanocytic cells with cross-reacting antigenic determinants, phagocytic cells containing melanocyte antigens, or possibly melanocytes or melanocyte stem cells liberated at the time of biopsy of the cutaneous melanoma. Examination of SLN requires careful correlation of H+E and IHC findings.

Prognostic significance of isolated HMB45 or Melan A positive cells in Melanoma sentinel lymph nodes

The detection of micrometastases (defined as groups of malignant cells) in the sentinel lymph node (SLN) is an important prognostic tool in melanoma. The use of immunohistochemistry with melanocytic markers such as HMB45 and Melan A increases the detection rate of micrometastases but there are also cases with isolated immunohistochemically positive cells (IPC). To determine the prognostic significance of isolated HMB45 and/or Melan A positive cells in melanoma SLN, we compared the clinical course of 47 patients with IPC to 308 patients with negative SLN and to 122 patients with micrometastases. The mean follow-up was 38.1 months. By Kaplan-Meier analyses, relapse free survival and overall survival of patients with IPC were similar to SLN negative patients, whereas patients with micrometastases had a significantly worse relapse free survival and overall survival. In the 47 patients with IPC, 6 relapses (12.8%) and 3 melanoma-related death (6.4%) occurred, in the SLN negative patients 36 relapses (11.7%) and 17 melanoma-related deaths (5.5%), in the patients with micrometastases 46 relapses (37.7%) and 29 melanoma-related deaths (23.8%). Prognosis of patients with IPC in SLN did not correlate with type of positive staining (HMB45, Melan A, or both), capsular involvement, number of cells, presence of cytologic atypias of IPC, or tumor penetrative depth. In conclusion, with short-term follow-up IPC in melanoma SLN are without prognostic significance.

Prognostic significance of histopathological parameters in sentinel nodes of melanoma patients

AIMS

The presence of micrometastases in the sentinel lymph node (SLN) is an important prognostic parameter for melanoma patients. The aim was to determine the prognostic relevance of histopathological characteristics of micrometastases in the SLN, which has not been adequately addressed thus far.

METHODS AND RESULTS

In 169 melanoma patients with positive SLN, histopathological features of the SLN were correlated with overall survival (OS) and relapse-free survival (RFS). Tumour burden, expansion of melanoma cells in the periphery (infiltration of capsule) and towards the centre of the SLN [tumour penetrative depth (TPN)] were of prognostic significance for OS and RFS on univariate analysis. Multivariate analysis revealed three independent significant parameters which predict a poor prognosis: presence of infiltration of the SLN capsule, TPN > or = 2 mm and size of the largest tumour deposit > or = 30 cells.

CONCLUSIONS

Histopathological analysis of SLN allows the identification of patients with a poor prognosis depending on the location of melanoma cells and tumour burden.

Diagnosis and treatment of cutaneous melanoma: state of the art 2006*

Although the incidence of melanoma is still rising in Caucasian populations, the increase in mortality has leveled off. Improvements in early diagnosis, with more frequent diagnosis of low-risk patients (i.e. those with <1 mm of tumor thickness), is the main reason for these divergent developments. Primary prevention has not yet been successful and recent studies have demonstrated the lack of effectiveness of sunscreen in preventing nevi in children. Progress was made in early melanoma diagnosis when dermoscopy and digital dermoscopy were introduced, and computer algorithms have proved to be highly efficacious for automated melanoma diagnosis. Primary melanomas are now excised with narrower surgical margins of 1-2 cm. Sentinel-node biopsy is recommended as a nodal staging procedure in patients with tumor thickness of 1 mm and more, but the prognostic impact of this procedure has not yet been demonstrated. New imaging techniques, e.g. whole-body MRI and PET-CT, provide more accurate staging, particularly in patients with apparent metastasis, and facilitate decisions on surgical treatment strategies. Staging is now based on the 2001 TNM classification including tumor thickness and histopathologic ulceration in stages I and II and lymph node micro and macro-metastasis in stage III. A stage- and risk-adopted follow-up schedule is proposed for melanoma surveillance. Adjuvant therapy with interferon-alpha in high-risk patients offers a small benefit in terms of recurrence-free and overall survival; the optimal dosage and duration of this treatment are still to be defined. Almost no progress has been made in the medical treatment of disseminated metastasis of melanoma. Therapy with dacarbazine and a few other single agents remains the first-line treatment approach of choice. A number of new treatment modalities, including targeted molecules and immunologic approaches with monoclonal antibodies, are under development; hopefully, new treatment modalities will be available in the near future.

Autoimmunity as a prognostic factor in melanoma patients treated with adjuvant low-dose interferon alpha

Interferon alpha is used for the adjuvant treatment of malignant melanoma at different dosages (high-, intermediate-, low-dose therapy). Only a minority of patients might benefit from this therapy, and markers to identify such patients are missing. A recent study suggested that melanoma patients developing autoantibodies or clinical manifestations of autoimmunity during adjuvant high-dose interferon alpha treatment had a significant survival benefit. We retrospectively reviewed 134 melanoma patients from our institution treated with adjuvant low-dose interferon alpha therapy and correlated the development of autoimmune diseases with prognosis. Interferon (IFN) therapy was routinely monitored by history, physical examination and laboratory tests before, after the first month and then after every 3 months of therapy. During a median follow up of 46.0 months (8.5-79.0 months) 28 patients (20.9%) suffered from recurrences and melanoma related deaths occurred in 16 patients (11.9%). In 20 patients (14.9%) autoimmune thyroiditis (AIT) was diagnosed during IFN therapy, one of these 20 patients developed rheumatoid arthritis later while continuing IFN therapy. Other autoimmune diseases were not observed. In 2 patients (one with AIT and one with arthritis) the autoimmune disease led to discontinuation of IFN therapy, in the other patients AIT remained subclinical or responded well to treatment while IFN therapy was continued. Kaplan-Meier analyses revealed a significant better recurrence free survival and a trend for a better overall survival for patients with AIT. Thus, autoimmunity triggered by low-dose IFN therapy appears to indicate an improved prognosis and should encourage continuation of IFN therapy.

Prospective Multi-Institutional Study of Reverse Transcriptase Polymerase Chain Reaction for Molecular Staging of Melanoma

Purpose

To evaluate the prognostic significance of molecular staging using reverse transcriptase polymerase chain reaction (RT-PCR) in detecting occult melanoma cells in sentinel lymph nodes (SLNs) and circulating bloodstream.

Patients and Methods

In this multicenter study, eligibility criteria included patient age 18 to 71 years, invasive melanoma ≥ 1.0 mm Breslow thickness, and no clinical evidence of metastasis. SLN biopsy and wide excision of the primary tumor were performed. SLNs were examined by serial-section histopathology and S-100 immunohistochemistry. A portion of each SLN was frozen for RT-PCR. In addition, RT-PCR was performed on peripheral-blood mononuclear cells (PBMCs). RT-PCR analysis was performed using four markers: tyrosinase, MART1, MAGE3, and GP-100. Disease-free survival (DFS), distant–DFS (DDFS), and overall survival (OS) were analyzed.

Results

A total of 1,446 patients with histologically negative SLNs underwent RT-PCR analysis. At a median follow-up of 30 months, there was no difference in DFS, DDFS, or OS between the RT-PCR–positive (n = 620) and RT-PCR–negative (n = 826) patients. Analysis of PBMC from 820 patients revealed significant differences in DFS and DDFS, but not OS, for patients with detection of more than one RT-PCR marker in peripheral blood.

Conclusion

In this large, prospective, multi-institutional study, RT-PCR analysis on SLNs and PBMCs provides no additional prognostic information beyond standard histopathologic analysis of SLNs. Detection of more than one marker in PBMC is associated with a worse prognosis. RT-PCR remains investigational and should not be used to direct adjuvant therapy at this time.

Novel genes associated with malignant melanoma but not benign melanocytic lesions

PURPOSE

Cutaneous melanoma is a common, aggressive cancer with increasing incidence. The identification of melanoma-specific deregulated genes could provide molecular markers for lymph node staging assays and further insight into melanoma tumorigenesis.

EXPERIMENTAL DESIGN

Total RNA isolated from 45 primary melanoma, 18 benign skin nevi, and 7 normal skin tissue specimens were analyzed on an Affymetrix Hu133A microarray containing 22,000 probe sets.

RESULTS

Hierarchical clustering revealed a distinct separation of the melanoma samples from the benign and normal specimens. Novel genes associated with malignant melanoma were identified. Differential gene expression of two melanoma-specific genes, PLAB and L1CAM, were tested by a one-step quantitative reverse transcription-PCR assay on primary malignant melanoma, benign nevi, and normal skin samples, as well as on malignant melanoma lymph node metastasis and melanoma-free lymph nodes. The performance of the markers was compared with conventional melanoma markers such as tyrosinase, gp100, and MART1.

CONCLUSION

Our study systematically identified novel melanoma-specific genes and showed the feasibility of using a combination of PLAB and L1CAM in a reverse transcription-PCR assay to differentiate clinically relevant samples containing benign or malignant melanocytes.

Sentinel node biopsy in melanoma delays recurrence but does not change melanoma-related survival: a retrospective analysis of 673 patients

BACKGROUND

The status of the sentinel lymph node (SLN) is an important parameter to predict the prognosis of melanoma patients but it is a matter of debate if removal of micrometastases by SLN biopsy (SLNB) influences the prognosis of melanoma patients.

OBJECTIVES

We sought to investigate the impact of SLNB in melanoma patients with regard to recurrence-free survival, overall survival and metastatic pathways.

PATIENTS AND METHODS

We studied, retrospectively, 673 melanoma patients with a primary melanoma (tumour thickness > or = 1 mm) and without clinical evidence of metastases at the time of melanoma diagnosis. In 377 patients the melanoma was removed without SLNB between January 1995 and March 2000 (pre-SLNB group). In 296 patients the melanoma was removed with SLNB between April 2000 and March 2003 (SLNB group). Otherwise, both groups received identical surgical treatment of the primary melanoma and initial staging procedures performed by the same team of physicians. Follow-up recommendations were also identical in both groups.

RESULTS

Both groups showed no significant differences with regard to characteristics of the primary melanoma, sex and age. By Kaplan-Meier analyses, melanoma-related overall survival was comparable in both groups. However, recurrence-free survival was increased in pre-SLNB patients due to significantly fewer regional lymph node metastases, whereas frequencies of locoregional cutaneous and distant metastases were comparable in both groups.

CONCLUSIONS

SLNB advances the detection of regional lymph node metastases and therefore avoids nodal recurrences but does not influence metastatic behaviour of melanoma cells and does not protect patients from melanoma-related death caused by distant metastases. Thus, our retrospective data favour the marker hypothesis for melanoma metastasation. To elucidate further if subgroups of patients benefit from SLNB, prospective randomized studies with long-term follow-up are needed.

Pathologic assessment of melanoma sentinel nodes: a role for molecular analysis using quantitative real-time reverse transcription-PCR for MART-1 and tyrosinase messenger RNA

PURPOSE

Molecular analysis of melanoma sentinel nodes (SN) is sensitive, but poorly specific because metastases cannot be distinguished from benign nevus inclusions (BNI). We investigated whether quantitative reverse transcription-PCR (RT-PCR) detection of MART-1 and tyrosinase mRNAs could improve this specificity and contribute to SN assessment.

EXPERIMENTAL DESIGN

Two hundred twenty SNs from 95 melanoma patients analyzed by extensive immunohistopathology and real-time quantitative RT-PCR.

RESULTS

Using histopathology, SNs and patients were allotted to three diagnostic groups: (a) metastasis positive, (b) BNI positive, and (c) melanocyte-free. Median MART-1 and tyrosinase mRNA levels in SNs were significantly different in patients with metastasis compared with patients with BNIs (P < 0.05) and patients without melanocytic lesions (P < 0.001). However, a "gray-zone" was observed where distinction, based on mRNA levels, could not be made between the three groups. For both genes, the highest mRNA level recorded in each RT-PCR-positive patient was positively correlated with Breslow's tumor thickness. For SNs with metastases, tumor burden was significantly correlated to the mRNA level. Using the presence of a MART-1 RT-PCR signal to detect patients with metastases, a sensitivity of 100% and a negative predictive value of 100% were achieved when extensive immunohistology was used as reference.

CONCLUSIONS

Quantitative RT-PCR MART-1 and tyrosinase mRNA analysis cannot be used alone for SN diagnosis because of its poor specificity for melanoma metastasis. However, in approximately one third of cases without RT-PCR evidence of MART-1 expression, extensive histopathologic SN investigation is not necessary, thus substantially reducing the cost of SN analysis. The level of melanocyte-associated mRNA is associated with both tumor thickness and tumor burden as measured histopathologically, suggesting that this may be of prognostic value.

[Malignant melanoma -- a medical students' viewpoint]

Malignant melanoma is a primarily cutaneous melanocytic tumour with increasing incidence responsible for 90 % of skin cancer mortality. Genetic predisposition has been identified as the most important risk factor, while UV is second in importance and can be avoided. New diagnostic methods include sentinel lymph node biopsy and the detection of tumour markers in blood. Furthermore, malignant melanoma shows an extraordinary resistance to therapy; at present the only cure lies in early excision of the primary tumour. Thus early recognition is of utmost importance. Experimental approaches, such as dendritic cell vaccination, have shown some effectiveness which must be confirmed in multicenter, randomised trials.

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.

Pathologic analysis of sentinel lymph nodes in melanoma patients: Current and future trends

Sentinel lymph node dissection (SLND) has become the standard of care for the staging of clinically-node negative melanomas and breast cancers. A large literature documents the efficacy of SLND in the staging of melanoma and breast cancer. The SLND has lower associated patient morbidity in comparison to elective node dissections that remove the closest regional-draining node group. SLND has improved accuracy over traditional regional node dissection for the staging of melanoma. Currently, several multicenter trials are evaluating the prognostic significance of melanoma micrometastases in SLN detected by immunohistochemical and molecular methods. Pending trial outcome analysis, SLND has no proven effect on mortality. However, given the current oncologic emphasis on detection and removal of nodal tumor metastases, the technique has an important role in minimizing the invasiveness of tumor staging for melanoma and breast cancer. As long as lymph node metastases are used for staging solid malignancies, surgical pathologists are likely to encounter SLN excisional biopsies as a part of their routine practice.

Sentinel lymph nodes in malignant melanoma

BACKGROUND

The optimal technique for sentinel lymph node (SN) assessment in patients with melanoma is controversial. Molecular analysis (reverse transcriptase-polymerase chain reaction) detects significantly greater numbers of SNs with suspected micrometastases (up to 71%) than does routine histopathology (approximately 20%). The authors sought to identify possible reasons for this discrepancy and to determine whether using an extended histopathologic protocol could improve diagnostic precision.

METHODS

Two hundred thirty-one SNs from 100 consecutive patients with cutaneous melanomas that measured 1-4 mm in thickness were bisected, and half of the lymph node was examined according to an extensive histopathologic protocol involving serial sectioning and immunohistochemical analysis of 3 melanocyte-associated markers (S-100, HMB-45, and Melan-A).

RESULTS

Lymph node melanocytic lesions were frequent, with micrometastases and benign nevus inclusions (BNI) found in SNs in 28% and 28% of patients, respectively (4 SNs contained both). Melan-A was the most sensitive immunohistochemical marker and was positive in all BNI-positive SNs and 97% of micrometastasis-positive SNs. Although HMB-45 showed differential labeling in micrometastases compared with BNI (82% vs. 16%), immunohistochemistry could not distinguish between those lesions. Micrometastases were already identified on the first central level in 49% of positive SNs, whereas only 23% of SNs with BNI were diagnosed on the first level.

CONCLUSIONS

Extensive serial sectioning with immunohistochemical analysis substantially increased the histopathologic detection of micrometastases and BNI in melanoma SNs to a level approaching the level reported for molecular techniques. The large number of BNIs represents an important potential source of imprecision (false positivity) in SN assays based on nonmorphologic methods.