CCND1 copy number increase and cyclin D1 expression in acral melanoma: a comparative study of fluorescence in situ hybridization and immunohistochemistry in a Chinese cohort

Background CCND1 copy number increase is characteristic of acral melanoma and is useful in distinguishing benign and malignant acral melanocytic lesions. Increase of the gene copy number may result in protein overexpression. This raises the possibility that detection of high expression of cyclin D1 by immunohistochemistry (IHC) may be used as a surrogate for direct evaluation of increase in the CCND1 gene copy number. Methods We examined increases in CCND1 copy number with fluorescence in situ hybridization (FISH), and examined cyclin D1 protein expression with IHC in 61 acral melanomas. Results Using FISH, 29 acral melanomas (29/61, 47.5%) showed increase in the CCND1 copy number, including 8 (8/61, 13.1%) which showed low-level increase in the CCND1 copy number and 21 (21/61, 34.4%) with high-level increase in the CCND1 copy number. By analysis of IHC, the median IHC score was 15% (range: 1-80%) in acral melanomas with no CCND1 copy number alteration. In acral melanomas with low-level CCND1 copy number increase, the median IHC score was 25% (range: 3-90%). In acral melanomas with high-level CCND1 copy number increase, the median IHC score was 60% (range: 1-95%). Comparing FISH and IHC, cyclin D1 protein expression level has no corelation with the CCND1 copy number in acral melanomas which have no CCND1 copy number alteration and low-level CCND1 copy number increase (P = 0.108). Cyclin D1 protein expression level correlated positively with CCND1 copy number in acral melanomas with high-level CCND1 copy number increase (P = 0.038). The sensitivity, specificity and positive predictive value of using cyclin D1 IHC to predict CCND1 FISH result was 72.4, 62.5 and 63.6%. Increase in CCND1 copy number was associated with Breslow thickness in invasive acral melanoma. Conclusion High-level increase in the CCND1 copy number can induce high cyclin D1 protein expression in acral melanomas. However low-level increase and normal CCND1 copy number have no obvious correlation with protein expression. Cyclin D1 IHC cannot serve as a surrogate for CCND1 FISH in acral melanomas.