To evaluate the diagnostic sensitivity of fluorescence in situ hybridization (FISH) using probes targeting 6p25, 6q23, 11q13, and Cep6 in melanoma subtypes. Design: Blinded comparison of chromosomal copy number changes detected using FISH targeting 6p25, 6q23, 11q13, and Cep6 in benign nevi and melanoma subtypes.

Nevoid melanoma may resemble benign compound or intradermal nevi by their silhouette and profile on low power. Higher power usually reveals nuclear atypia, confluence of cells, incomplete maturation and dermal mitotic activity. However, to some extent all of these features maybe seen in benign compound or intradermal nevi and no single criteria can be used to differentiate nevoid melanoma from a benign nevus. The distinction can be particularly problematic in nevi that show mitotic activity and we have noted a recent trend in diagnosis of melanocytic neoplasms with dermal mitosis as nevoid melanoma despite the presence of normal maturation in the dermis and lack of significant nuclear atypia. Therefore in this study we evaluated 10 nevoid melanomas, 4 of which resulted in metastasis and 10 mitotically active nevi with fluorescence in situ hybridization targeting key chromosomal loci previously shown to effectively discriminate been malignant and benign melanocytic neoplasms. All 10 nevoid melanomas showed copy number abnormalities by fluorescence in situ hybridization in either chromosome 6 or 11 while none of the 10 mitotically active nevi did. The results demonstrate that fluorescence in situ hybridization targeting key chromosomal loci on chromosomes 6 and 11 can be effective in discriminating nevoid melanomas from mitotically active nevi. Additionally, our study presents further evidence that dermal mitoses alone without other diagnostic features such as nuclear atypia and lack of maturation does not constitute sufficient evidence alone for a diagnosis of melanoma.

Blue nevus (BN)-like cutaneous melanoma metastasis is a well-recognized variant of melanoma metastasis. These lesions may clinically and histologically simulate benign blue nevi. The histologic changes may be indistinguishable from conventional blue nevi or epithelioid blue nevi (EBN), a benign dermal-based melanocytic neoplasm with epithelioid morphology and heavily pigmented cytoplasm. Distinguishing BN-like cutaneous melanoma metastasis from benign conventional or EBN is important for staging and treatment. We evaluated a fluorescence in situ hybridization (FISH) assay using probes targeting 6p25 (RREB1), 6q23 (MYB), 11q13 (CCND1), and centromere 6 (Cep6) with previously determined criteria, to distinguish EBN and BN-like melanoma metastasis. Ten BN-like cutaneous melanoma metastatic lesions and 10 EBN were blindly evaluated with the above mentioned FISH probes. FISH enumeration and criteria for diagnosis of melanoma was as previously described. Nine of 10 BN-like cutaneous metastatic lesions showed significant aberrations and met previously established criteria for melanoma. None of the EBN cases showed evidence of significant copy number changes or met FISH criteria for a diagnosis of melanoma. FISH is an important diagnostic adjunct for melanocytic neoplasms. In this study, we show that a FISH assay targeting 6p25, 6q23, 11q13, and centromere 6 can distinguish EBN from BN-like metastatic melanoma with high accuracy. The test and the parameters previously established can perform with high sensitivity and specificity when dealing with this differential diagnosis.

Up to 30-50% of melanomas arise in association with a nevus. Accurately defining, the nevus from the melanoma can significantly affect microstaging. Recently, we showed that a targeted fluorescence in situ hybridization (FISH) assay could distinguish between benign nevi and melanoma with a sensitivity of 87% and specificity of 95%. In this study, we evaluated the potential of this same assay for use in the microstaging of melanoma. We performed FISH on 36 cases of melanoma occurring in association with a nevus and 6 cases of nevoid melanoma with deep dermal involvement. In the melanomas with associated benign nevi, FISH enumeration was performed separately on the histologically malignant and benign components. In the nevoid melanomas, FISH was performed on the deep dermal areas. On the basis of the criteria developed in our earlier studies, we determined the sensitivity of the assay within the malignant areas and the specificity within the benign areas of melanomas with associated nevi. In addition, we evaluated the sensitivity and specificity within a group of six nevoid melanomas with deep dermal involvement. Among melanomas with associated nevi, 28 of 36 cases (78%) tested positively in the histologically malignant areas. The benign nevus components were uniformly negative for all criteria. Six of six nevoid melanomas (100%) tested positively in the deep dermal area. FISH analysis with probes targeting 6p25, 6q23, 11q13 and CEP6 can effectively discriminate the malignant and benign components of melanomas with associated nevi and can be used as an adjunctive tool for microstaging. The assay has high sensitivity for the malignant areas of nevus-associated melanomas and outstanding specificity for the benign areas. The sensitivity is independent of the morphological features, and the assay performs well in nevoid melanoma cases.

No abstract