Clinical size is a poor predictor of invasion in melanoma of the lentigo maligna type.

BACKGROUND: There are no well-defined clinical factors to predict the risk of occult invasion in melanoma of the lentigo maligna type (LM) before complete histopathologic analysis. OBJECTIVE: To evaluate whether clinical size was a predictor of invasion in LM and subclinical extension. METHODS: Consecutive cases of LM were recorded in a prospectively maintained database from 2006 to 2019. Patient and tumor data were recorded during initial evaluation. The LM clinical area was calculated in square millimeters (length × width). All patients were treated with staged excision. RESULTS: We included 600 patients. The mean age was 65.9 years (standard deviation, 12.3; range, 27-95 years); 62.8% (n = 377) were men. The mean LM clinical area was 128.32 mm2 for in situ lesions versus 200.14 mm for invasive lesions (P = .1). Based on quantile regression, the median margin required for complete removal increased with LM clinical area. LIMITATIONS: The study was performed in a tertiary cancer center with possible referral bias and more complex cases. CONCLUSIONS: LM can present with variable clinical size, which may correlate with subclinical extension; however, the presence of invasion is not well estimated by LM clinical area.