Fluorescence in situ hybridization, a diagnostic aid in ambiguous melanocytic tumors: European study of 113 cases

Abstract

Some melanocytic tumors are ambiguous, so the reproducible histopathological diagnosis of benign or malignant lesion is difficult. This study evaluated the contribution of fluorescence in situ hybridization (FISH) first in 43 non-equivocal melanomas and nevi, and then in 113 ambiguous melanocytic tumors selected by expert pathologists from six different European institutions. We included two groups of ambiguous tumors: patients without recurrence (5-year minimal follow-up) and with metastases. An independent triple-blind histopathological review was performed to classify tumors as 'favor benign' (AÀ) or 'favor malignant' (A þ ). A four-color probe set targeting 6p25, 6q23, 11q13 and CEP6 was used for FISH. In the 43 non-equivocal melanomas and nevi, sensitivity was 85% and specificity 90%. Ninety out of 95 ambiguous melanocytic tumors included were FISH interpretable (67 FISH negative and 23 FISH positive). Of the 90 patients, 69 presented no recurrence and 21/90 exhibited metastases. These ambiguous tumors were mostly spitzoid tumors (45/90). Histopathological reviewers classified these tumors as favor malignant (49/90) and favor benign (32/90), whereas nine cases had a discordant diagnosis. By comparison with outcome, the sensitivity and specificity of histopathological review were 95 and 52%, and the sensitivity and specificity of FISH were 43 and 80%. Compared with histopathological review, the sensitivity and specificity of FISH were 34.5 and 91%. Interestingly, by combining the histopathological diagnosis with FISH results, the diagnosis was optimized, especially by increasing specificity (76% instead of 52% for expert diagnosis alone) and by improving sensitivity compared with FISH alone (90 vs 43% for FISH result alone). The value of this FISH test is to add a reproducible demonstration of malignancy to the histopathological diagnosis, especially in doubtful/ambiguous melanocytic tumors. A positive FISH test reinforces the diagnosis of melanoma, allowing such tumors (particularly thick tumors) to be managed as melanomas.

Histological and genetic evidence for a variant of superficial spreading melanoma composed predominantly of large nests

“…The 4-probe FISH test has been reported to have a sensitivity and specificity of 85-90% for the The commercially available melanoma FISH probe set, which covers only three loci on chromosome 6 (RREB1, CEP6, and MYB) and one locus on chromosome 11 (CCND1), was negative in this case. diagnosis of melanoma, 5,6 but is of limited utility in the assessment of histologically ambiguous melanocytic skin tumors. 12 Although the aCGH profiles correlated well with the morphological features of MLN, the correlation with FISH was poorer.…”

“…1 Although histological evaluation is a reliable means of accurately classifying melanocytic tumors as benign (nevi) or malignant (melanoma), this distinction can be difficult in a minority of cases. Based on the fact that melanomas are characterized by chromosomal aberrations, molecular genetic tests such as comparative genomic hybridization (CGH) [2][3][4] and fluorescence in situ hybridization [5][6][7][8] have been shown to be useful ancillary techniques, which assist accurate classification of melanocytic tumors. Multiple chromosomal gains and losses are identified with CGH in the majority (495%) of melanomas, whereas melanocytic nevi typically lack chromosomal aberrations.…”

An independent validation of a gene expression signature to differentiate malignant melanoma from benign melanocytic nevi

“…The sensitivity and specificity of the FISH method varies dramatically among existing reports with the lesion subtype, the probe set used, the number of observers, and the cutoff thresholds used. Various authors have reported a FISH sensitivity ranging from 43% to 94% and a specificity ranging from 60% to 98% 24, 25, 26, 27, 28. The original 4‐probe FISH assay targeting 6p25 (RREB1), 6q23 (MYB), Cep6 (centromere 6), and 11q13 (CCND1) was reported to discriminate between histologically unequivocal melanomas and benign nevi with a sensitivity of 86.7% and a specificity of 95.4% 24.…”

Comparison between melanoma gene expression score and fluorescence in situ hybridization for the classification of melanocytic lesions

“…The diagnostic utility of FISH is controversial in the setting of such ambiguous melanocytic lesions, where the overall reported sensitivity lies between 43 and 100% and the specificity between 33 and 83% using clinical behavior or expert histopathologic review as the gold standard. 6,[16][17][18][19] Of note, within spitzoid tumors, FISH testing has a low sensitivity in detecting spitzoid melanoma around 70%. Thus, to improve on the diagnostic sensitivity and specificity and to overcome the limitations imposed by tetraploidy, probes for 9p21, a region homozygously deleted in a subset of spitzoid melanomas, and for 8q24, the gain of which is associated with poorer outcome, were integrated into the standard FISH panel to increase the diagnostic sensitivity and specificity of the assay and add prognostic relevance.…”