Correlation of Inflammation in Frozen Sections With Site of Nonmelanoma Skin Cancer.

IMPORTANCE: During Mohs micrographic surgery of nonmelanoma skin cancer (NMSC), inflammation in histologic frozen sections has been found to occasionally presage the detection of tumors in frozen sections of adjacent excision specimens. OBJECTIVE: To quantify the correlation between the location of inflammation without visible tumor in histologic frozen sections and the location of subsequently detected NMSC. DESIGN, SETTING, AND PARTICIPANTS: A retrospective cohort study of 3148 cases pertaining to frozen sections associated with the staged excision of NMSC was performed from September 8, 2008, to September 18, 2009, at an urban academic medical center, with the collected data analyzed on May 9, 2013. EXPOSURES: Consecutive cases of Mohs micrographic surgery performed at an academic medical center. MAIN OUTCOMES AND MEASURES: For each wedge-shaped tissue segment corresponding with 1 hour of time on a clock face, the proportion of patients with inflammation at the source location of the segment who subsequently had a tumor at this same location; the proportion of patients who had neither inflammation nor subsequent tumor at the source location of the segment; the probability of subsequent tumor at this location given the prior finding of inflammation at the same location; and the probability that a location was without tumor in the absence of preexisting inflammation at that location. RESULTS: Of the medical records of 3148 cases of NMSC that were reviewed, 60 showed inflammation in histologic frozen sections from an excision specimen that was followed by tumor in the subsequent excision specimen. Of these 60, 39 (65%) were b asal cel carcinoma and 21 (35%) were squamous cell carcinomas; 53 (88%) were Mohs stage 1. In 7 of 12 segments, a significant positive correlation was found between the presence of inflammation and the presence of nearby tumor with correlation coefficients ranging from 0.196 to 0.384 (P < .05) . The probability that tumor was absent when inflammation was not seen at a particular location (ie, clock-face segment) in preceding sections from that location was 91%, with segment-specific probability values ranging from 82% to 96%. CONCLUSIONS AND RELEVANCE: During Mohs micrographic surgery of NMSC with the examination of frozen sections, histologic inflammation is modestly predictive of adjacent tumor whereas lack of inflammation strongly predicts that no additional tumor will be found.