Application of fluorescence in situ hybridization in distinguishing acral melanoma in situ from acral junctional melanocytic nevus on the volar skin in Japanese patients

Four‐colored fluorescence in situ hybridization (FISH) is an ancillary diagnostic tool for melanoma. However, most studies that have investigated the usefulness of FISH primarily focused on advanced melanomas. The aim of the current study was to evaluate the effectiveness of FISH in distinguishing acral melanoma (AM) in situ from benign acral junctional nevus (AJN), two types of lesions that are difficult to differentiate via traditional clinical means. The authors investigated the usefulness of FISH in 91 acral melanocytic lesions, including 50 lesions with diagnostic discrepancies between dermoscopic and pathologic approaches or difficulty diagnosing between AM in situ and AJN, on the volar skin of Japanese patients. The authors classified the lesions based on the diagnosis of dermatologists and pathologists into four groups: (I) lesions with a unanimous diagnosis by dermatologists and pathologists as AM in situ or AJN (n = 41); (II) lesions with a unanimous diagnosis by dermatologists only as AM in situ or AJN (n = 21); (III) lesions with a unanimous diagnosis by pathologists only as AM in situ or AJN (n = 15); and (IV) all other lesions (n = 14). The dermatologists diagnosed the lesions by clinical and dermoscopic photographs alone, while the pathologists diagnosed the lesions by microscopy of hematoxylin and eosin–stained slides alone. In group I (AM in situ [n = 20] and AJN [n = 21]), four‐colored FISH demonstrated 90% sensitivity and 81% specificity in distinguishing AM in situ from AJN. There was a significant correlation between the FISH results and the unanimous diagnoses by pathologists alone (p = 0.03) in group III. However, FISH results were not significantly correlated with the unanimous diagnoses by dermatologists alone (p = 0.33) in group II. In conclusion, the four‐colored FISH probe kit was useful in distinguishing between AM in situ and AJN and may be an ancillary method when pathologists who are not experts of dermatopathology diagnose melanocytic lesions.