Cutaneous melanomas exhibiting unusual biologic behavior.

In rare instances, primary malignant melanoma thickness fails to predict the biologic course of the disease: lesions less than 0.8 mm thick may recur locally or metastasize, lesions greater than 5.5 mm thick may not prove to be fatal within the expected interval of time, and melanoma recurrences may develop greater than 10 years after first definitive melanoma treatment. The large Sydney Melanoma Unit data base of over 9,500 patients treated over a 41-year period provided a unique opportunity to study the characteristics and prognosis of these patients with unusual melanomas. In stage I patients with thin lesions, and no sign of disease elsewhere, presence of ulceration, high mitotic activity, and/or penetration into the reticular dermis predisposed these melanomas to recur and regression did not emerge as a risk factor for recurrence. This was in sharp contrast to the histology of the thin lesions in patients with concurrent regional lymph node metastases (stage II). Moderate to severe regression was present in all the latter lesions, ulceration and mitoses were absent, and none penetrated beyond the papillary dermis. No specific criteria were found that could identify those stage I or II patients with thick melanomas but at low risk for recurrence or those patients with localized disease (stage I) who required long-term follow-up beyond 10 years. These results indicate that guidelines for follow-up of melanoma patients after first definitive treatment may not be appropriate for a small proportion of patients.(ABSTRACT TRUNCATED AT 250 WORDS)