Long-Term Survival of Patients with Thin (T1) Cutaneous Melanomas: A Breslow Thickness Cut Point of 0.8 mm Separates Higher-Risk and Lower-Risk Tumors.

BACKGROUND: Counterintuitively, more deaths from melanoma occur among patients with thin (T1) primary melanomas (≤ 1 mm) than among those with thick primary melanoma because the great majority present with T1 tumors. Therefore, it is important to stratify their risk as accurately as possible to guide their management and follow-up. This study sought to explore the relationship between tumor thickness and prognosis for patients with thin primary melanomas.
METHODS: A retrospective, single-institution study investigated 6263 patients with cutaneous melanoma (including 2117 T1 cases) who had a minimum follow-up period of 10 years.
RESULTS: For the entire patient cohort, the 10-year melanoma-specific survival (MSS) rate ranged between 92% for the patients with primary melanomas up to 0.3 mm thick and 32% for those with melanomas thicker than 8 mm. When divided into 25-quantile-thickness groups there was a significant difference in 10-year MSS between the two consecutive groups 0.8 and 0.9 mm; the differences in survival were not significantly different for any other consecutive cut points within the less than or equal to 1 mm thickness range, indicating a biologically-relevant difference in outcome above and below 0.8 mm. For the patients treated initially at the authors' institution, the 10- and 20-year MSS rates for those with tumors up to 0.8 mm thick were respectively 93.4 and 85.7%, and for tumors 0.9 to 1.0 mm, the rates were respectively 81.1 and 71.4%. Only 29.3% of the T1 patients who died of melanoma were deceased within 5 years.
CONCLUSIONS: A naturally occurring thickness cut point of 0.8 mm predicts higher or lower risk for patients with thin primary cutaneous melanomas. Long-term follow-up assessment of patients with T1 melanoma is important because late mortality due to melanoma is more common than early mortality.