Basal cell carcinoma: variation in invasion depth by subtype, sex, and anatomic site in 4,565 cases

The depth of invasion by basal cell carcinoma (BCC) subtypes varies.

To investigate BCC invasion depth variation by subtype and anatomic site.

A prospective consecutive case series of excised BCC from 2009 to 2014 in a single Australian clinic.

Descending mean depths for a total of 4,565 BCC cases by subtype were as follows: nodulocystic, 1.9 mm (n = 84, 95% CI: 1.70-2.03, P = 0.66); nodular, 1.6 mm (n = 947, 95% CI: 1.53-1.63, P < 0.0001); aggressive, 1.5 mm (n = 925, 95% CI: 1.44-1.59, P < 0.0001); superficial combined with nodular, 0.9 mm (n = 1,081, 95% CI: 0.83-0.90, P < 0.0001); and superficial, 0.3 mm (n = 1,528, 95% CI: 0.32-0.36, P < 0.0001). Deeper invasion was associated with increased chronic sunlight exposed sites. The deepest aggressive BCCs occurred on the neck with a mean depth of 1.8 mm (n = 46, 95% CI: 1.47-2.21).

We found significant differences in the depth of invasion for BCCs by sex, subtype, and anatomic site. For BCC with characteristics matching this study, overall adequate microscopic excision depths are proposed: superficial, 1.0 mm; superficial combined with nodular, 2.0 mm; nodular, 3.0 mm; and aggressive, 3.0 mm.