Cutaneous melanomas that defy conventional prognostic indicators.

Tumor thickness is usually an accurate prognostic indicator for the patient with melanoma. However, very thin primary melanomas occasionally recur locally or metastasize, whereas some patients with very thick primary melanomas survive far longer than expected. There is also a group of patients with primary melanomas of various thicknesses who relapse after a very long disease-free interval. The large database of the Sydney Melanoma Unit which now contains comprehensive long-term follow-up on more than 13,000 patients treated over a 45-year period, has provided a unique opportunity to study melanomas that defy conventional prognostic indicators. Recurrence developed in 2.8% of melanoma patients classified as stage I (pTNM staging system) and with very thin lesions (< 0.50 mm). These recurrences developed more frequently in women than men and histologically were found to be associated with ulceration, high mitotic activity, and invasion to Clark's level IV, but not with regression. Concurrent lymph node metastases (stage III) were present in 3.1% of patients with very thin lesions (< 0.50 mm). In this group, most patients were men, and every lesion displayed regression. Total survival exceeded 15 years in 15.7% of stage II and III patients with very thick lesions (> 5.5 mm). In 1.7% of patients with lesions of any thickness, the disease-free interval before relapse was > 15 years. Neither in patients with very thick lesions surviving for > 15 years, nor in those with a disease-free interval of > 15 years was it consistently possible to show the presence or absence of any of the histological features usually considered to be of prognostic significance.