Purpose: Most patients with melanoma have microscopically thin (< or = 1 mm) primary lesions and are cured with excision. However, some develop metastatic disease that is often fatal. We evaluated established prognostic factors to develop classification schemes with better discrimination than current American Joint Committee on Cancer (AJCC) staging.
Patients and methods: We studied patients with thin melanomas from the US population-based Surveillance, Epidemiology, and End Results (SEER) cancer registry (1988 to 2001; n = 26,291) and those seen by the University of Pennsylvania's Pigmented Lesion Group (PLG; 1972 to 2001; n = 2,389; Philadelphia, PA). AJCC prognostic factors were thickness, anatomic level, ulceration, site, sex, and age; PLG prognostic factors also included a set of biologically based candidate prognostic factors. Recursive partitioning was used to develop a SEER-based classification tree that was validated using PLG data. Next, a new PLG-based classification tree was developed using the expanded set of prognostic factors.
Results: The SEER-based classification tree identified additional criteria to explain survival heterogeneity among patients with thin, nonulcerated lesions; 10-year survival rates ranged from 89.1% to 99%. The new PLG-based tree identified groups using level, tumor cell mitotic rate, and sex. With survival rates from 83.4% to 100%, it had better discrimination.
Conclusion: Prognostication and related clinical decision making in the majority of patients with melanoma can be improved now using the validated, SEER-based classification. Tumor cell mitotic rate should be incorporated into the next iteration of AJCC staging.