SAN DIEGO – Histology of basal cell carcinomas removed by Mohs micrographic surgery showed that presurgical biopsies had not revealed all tumor subtypes in 64% of cases, and had underestimated the aggressiveness of the tumors 24% of the time, according to data from a large, multicenter, retrospective study.
“Unfortunately, while cheap and cost-effective, biopsies are a subsample of the full malignancy,” said Dr. Murad Alam, professor of dermatology, otolaryngology, and surgery at Northwestern University in Chicago. “Skin biopsy of basal cell carcinoma [BCC] may fail to detect all BCC subtypes, and as such may underestimate the aggressiveness of an individual BCC tumor.”
Basal cell carcinoma is the most common skin cancer worldwide, and can broadly be grouped into aggressive and indolent types, Dr. Alam said at the annual meeting of the American Society for Dermatologic Surgery. But tumors often show mixed histology, and cancer treatment needs to target the most aggressive subtype present in the tumor, he added. Results of past studies suggested that biopsies of BCCs could miss tumor subtypes, but the current research is the first large, multicenter study to confirm these findings, he and his associates said.
For the study, the investigators compared biopsy reports and microscopic slides of Mohs micrographic surgery (MMS) specimens from 871 consecutive cases of BCC treated at three hospitals in Illinois from 2013 to 2014. Patients first underwent biopsies, followed by complete excision of their tumors during MMS. Almost 59% of patients were male, and tumors were most commonly removed from the nose or cheek. In all, 78% of biopsies were obtained by the shave technique, but punch and excisional biopsies also were performed, the researchers noted.
Using standard definitions of BCC subtypes, the investigators compared levels of concordance between biopsy and MMS histology findings, Dr. Alam said. They also grouped tumor specimens as high risk (that is, infiltrative, morpheic, micronodular, basosquamous) or low risk (superficial or nodular), and determined whether tumor biopsy and MMS histology yielded the same or discordant risk assessments, he added.
Biopsies identified only 18% of tumors as being of mixed histology, compared with 57% of MMS specimens, said Dr. Alam. Biopsy results matched MMS histologies in only 31% of cases, while in 64% of cases, the MMS specimen yielded more tumor subtypes than the biopsy specimen. The researchers noted that biopsy yielded more subtypes than did MMS in 4% of cases, and that MMS and biopsy subtypes were fully discordant in only four cases.
Dr. Alam and his associates declared no external funding sources or conflicts of interest.