HMB45 negative spindle cell malignant melanoma

Desmoplastic malignant melanoma (DMM) and spindle cell malignant melanoma (SCMM) form a continuum without a discrete separation. One feature characteristic of DMM is a negative reaction for HMB45, a marker for premelanosomes. Fifty-six cases of SCMM were stained with HMB45. The clinical features, histologic features, and survival data for HMB45(+) and HMB45(-) SCMM were compared. Thirty cases were HMB45(-), and 26 were HMB45(+). In the HMB45(-) cases, there was a 1.4:1 ratio of males to females, and in the HMB45(+) cases the ratio was 1:1.5. Only 12.9% of the HMB45(-) cases occurred on the trunk compared with 40% of the HMB45(+) cases. The average ages for the HMB45(-) and the HMB45(+) cases were 65.6 and 61 years, respectively. Follow-up was obtained on 22 cases: 11 HMB45(-) and 11 HMB45(+). Of the 11 HMB45(-) cases, four had a 5-year disease-free survival. Of the 11 HMB45(+) cases, only one had a 5-year disease free survival. HMB45(-) SCMM appear to have a less aggressive biologic potential than HMB45(+) SCMM.