Comparison between lentigo maligna melanoma and other histogenetic types of malignant melanoma of the head and neck. Scottish Melanoma Group.

A study of 953 invasive cutaneous malignant melanomas of the head and neck was performed to determine differences between lentigo maligna melanoma and other histogenetic types with regard to patients and sites affected; prognosis was analysed in 595 of these cases. The cases studied comprised all head and neck melanomas registered with the Scottish Melanoma Group between 1979 and 1992, apart from the 3% of cases that were unclassifiable or rare histogenetic types. The histogenetic types of melanoma were 498 (52%) lentigo maligna melanoma (LMM), 237 (25%) superficial spreading melanoma (SSM) and 218 (23%) nodular melanoma (NM). All types increased in incidence throughout the study period. Patients with LMM (mean age 73 years) and NM (mean 68 years) were significantly older than those with SSM (mean 57 years). There were significant anatomical subsite differences related to sex of patients and histogenetic type of melanoma; melanomas on the face were more frequent in females and 90% of LMM occurred at this site, whereas melanomas on the scalp, neck and ears were more frequent in men. Kaplan-Meier estimates of the probability of survival were produced for the 595 of these 953 patients with 5 year follow-up details. In this group of patients the prognostic significance of tumour thickness, Clark level of invasion, ulceration, histogenetic type of melanoma and number of mitoses were studied using stepwise variable selection of procedures. Each of these possible prognostic factors attained individual significance but the tumour thickness was the dominant risk factor in the proportional hazards analysis. When patients were divided into four sex/ulceration subgroups (male/ulcerated, female/ulcerated, male/non-ulcerated, female/non-ulcerated) and analysed by proportional hazards analysis, no variable other than the tumour thickness had any further prognostic effect. Histogenetic type did not remain an independent prognostic variable at this stage. Despite sex and subsite differences, the prognosis for invasive lentigo maligna melanoma does not differ from that for other histogenetic types after controlling for tumour thickness.