Ancillary values of fluorescence in situ hybridization with different gene combination in diagnosis of malignant melanoma

Abstract

Objective: To investigate the clinical value of the first multicolor fluorescence in situ hybridization (FISH) assay on multiple genes, and combined with 9p21 and 8q24 evaluation in the differential diagnosis of melanoma. Methods: Fifty-six melanomas and 36 benign melanocytic nevi diagnosed in Fudan University Shanghai Cancer Center from 2017 to 2019 were included. Each specimen was examined by first multicolor FISH assay targeting 6p25 (RREB1), 6q23 (MYB), 11q13 (CCND1) and CEP6, as well as 9p21 (CDKN2A) and 8q24 (MYC). The results of FISH assay in all cases were recorded according to Gerami's criteria. Basing on the sensitivity and specificity of the first FISH assay, the refinement of diagnosis by adding combined 9p21 and 8q24 probes was further evaluated, as well as their association with different clinicopathological features. Results: In 86 cases, the FISH signals were adequate for analysis. Of the 56 melanoma cases, 52 cases were adequate for analysis; 36 cases (69.2%) were positive in the first FISH assay. The most frequent chromosomal anomaly was gain of RREB1 (30/52, 57.7%), followed by gain of CCND1 (20/52, 38.5%), loss of MYB relative to CEP6 (18/52, 34.6%) and gain of RREB1 relative to CEP6 (17/52, 32.7%). The frequency of homozygous deletions in 9p21 was 15.4% (8/52) and gain of 8q24 was 36.5% (19/52). Among the 36 melanocytic nevi cases, FISH results could be accurately evaluated in 34 cases, and none showed a positive result in the first FISH assay or 9p21 and 8q24 FISH analysis. Compared with the first FISH assay, the sensitivity of combination with 9p21 and 8q24 FISH analysis increased from 69.2% to 76.9% (40/52) and the specificity remained 100.0%. Statistical data showed that the rates of FISH positivity in patients with acral-lentiginious melanoma and nodual melanoma subtypes were higher than that in patients with superficial spreading melanoma and lentigo maligna melanoma subtypes, and patients with Breslow thickness>2.0 mm had higher positive FISH frequency than patients with Breslow thickness ≤2.0 mm. Conclusion: Multisite FISH analysis is a highly effective ancillary tool for the differentiation of unequivocal malignant from benign melanocytic lesions. By combining the first FISH assay with CDKN2A and MYC assay, the clinical utility of FISH analysis is further optimized in differential diagnosis of melanoma. Patients with Breslow thickness>2.0 mm, or acral-lentiginious melanoma and nodual melanoma subtypes tend to have higher FISH positivity. There remains a need to further explore the ancillary value of FISH analysis in diagnosis of ambiguous lesions.