Histopathologic assessment of depth of follicular invasion of squamous cell carcinoma (SCC) in situ (SCCis): Implications for treatment approach

Abstract

Squamous cell carcinoma in situ (SCCis) has been reported to involve the hair follicle epithelium. Deep follicular invasion is often cited as a cause of treatment failure. We sought to define the frequency and the depth of hair follicle invasion by SCCis. The study included both a retrospective review of intraoperative pathology specimens from 42 SCCis cases treated with Mohs micrographic surgery and a prospective evaluation of serially sectioned SCCis tissue from 12 additional patients. Pathology specimens were analyzed for follicular invasion of SCCis. SCCis invasion of the superficial hair follicle infundibulum was observed in 61.3% to 87.5% of cases in the 2 cohorts, whereas invasion of the isthmus and lower follicle was observed in only 8.3% to 12.5% of cases. In most tumors the depth of follicular invasion was comparable with the thickness of the surrounding epidermis. The maximum observed depth of follicular invasion was 0.82 mm. The study was performed on a limited number of cases referred for surgery at a single institution. Although SCCis invasion of the upper hair follicle infundibulum is common, deep invasion below the level of the surrounding epidermis is rare. This may have implications for optimal therapy of this condition.