Tumor-to-bone distance of invasive subungual melanoma: an analysis of 30 cases.

Subungual melanoma (SUM) is rare and represents approximately 2-3% and 20% of all cutaneous melanomas in Caucasians and Asians, respectively. Amputation has usually been performed for invasive SUM; however, not all invasive SUMs invade or attach to the distal phalanx. To investigate the possibility of non-amputative surgery for patients with invasive SUM, the distances between the deepest base of the melanoma cells and the bony surface in the surgical specimens of invasive SUM were measured. Thirty surgical specimens of invasive SUM were retrospectively reviewed. The contents of the specimens were as follows: 14 first toes, 10 thumbs, three second fingers, two third fingers, and one fifth finger. Four specimens showed bone invasion, and the tumor was attached to the bone in four specimens. The tumor-to-bone distance exceeded 0.9 mm in all the specimens with thicknesses <4 mm. In the non-ulcerated SUMs (nine specimens), only one SUM specimen showed bone attachment. There was a higher likelihood of bone attachment or invasion when tumor thickness (TT) exceeded 4 mm (Pearson chi-square test, P = 0.009; Fisher exact test, P = 0.004; student t test, 0.033). Univariate and multivariate analysis also revealed that thick TT had a statistically significant affect (odds ratio 1.807 and 1.865, 95% CI 1.11-3.01 and 1.11-3.13, P = 0.023 and 0.018). Non-amputative surgery may be possible for SUM tumors that are of intermediate-thickness. However, there has been little evidence demonstrating survival with non-amputative surgery for invasive SUM. A large, randomized, prospective clinical study is required to address this issue.