Squamous Cell Carcinoma In Situ With Occult Invasion: A Tertiary Care Institutional Experience

BACKGROUND The rate of occult invasive disease within biopsy-proven squamous cell carcinoma in situ (SCCIS) is not well defined. OBJECTIVE To examine the rate of occult invasion in SCCIS. METHODS An institutional-wide pathology database was retrospectively searched for "squamous cell carcinoma in situ" over a 6-year period, and the treatment modality and final pathology results were analyzed for evidence of invasion. In addition, consecutive tumor blocks from Mohs micrographic surgery (MMS) cases of SCCIS were prospectively analyzed for invasion. RESULTS The rate of occult invasion for biopsy-proven SCCIS treated with excision was 4.0% (N = 49) and for the MMS margins was 3.5% (N = 310). For the prospective MMS tumor block analysis, the rate of occult invasion was 10.1% (N = 69). No clinical factors (age, sex, location, or size) correlated with increased risk of invasion. All invasive SCCs detected were superficial and well differentiated. CONCLUSION The rate of occult invasion for biopsy-proven SCCIS ranged from 3.5% to 10.1%. The detected rate of invasion varies based on the method of excision and pathology processing of specimens. The rate of invasion should be considered when managing SSCIS.