Clinical Follow-up of Atypical Spitzoid Tumors Analyzed by Fluorescence In Situ Hybridization.

Many neoplasms with spitzoid features remain enigmatic, especially those with intermediate grade features or "atypical spitzoid tumors" (ASTs). Fluorescence in situ hybridization (FISH) has emerged as a complementary technique to conventional microscopy, with certain chromosomal patterns conveying diagnostic information. In this study, we examined 36 ASTs analyzed by FISH for specific abnormalities in chromosomes 6, 9, and 11. Aberrations were detected in 11 cases, 7 of which met FISH criteria for spitzoid melanoma. These had homozygous deletion of 9p21, partial deletion of 11q13, gain of 6p25, and gain of 11q13. All 3 patients with positive sentinel lymph nodes, including one with progression beyond the sentinel lymph node, had homozygous deletion of chromosome 9p21, but there were no deaths in an average of 28 months of follow-up of these cases. Other aberrations in the chromosomal pattern of ASTs were heterozygous deletion of 9p21, partial deletion of 6p23, and tetraploidy. We found that ASTs, including those eventually diagnosed as spitzoid melanoma, had a more indolent course in our cohort than conventional malignant melanoma. Moreover, the addition of FISH results led to a more definitive diagnosis in 7 cases, 4 of which had abnormalities on FISH consistent with spitzoid melanoma.