Removal of Incidental Skin Cancer During Mohs Micrographic Surgery Indicated for a Different Primary Tumor

Background: Mohs surgery is a tissue-sparing, microscopically controlled procedure used to treat biopsy-proven skin cancers. Because Mohs surgery allows for examination of the complete margin of each tissue layer removed, separate cancers can be treated concomitantly when identified. As early detection of skin cancer is beneficial for reducing morbidity, incidental tumors discovered during Mohs surgery are of significant interest.

Objective: Our objective was to determine the prevalence and characteristics of incidental skin cancers found during Mohs surgery.

Methods: A retrospective chart review of cases seen at University of California, San Diego, from 2014 to 2021 was performed.

Results: Of 13,464 Mohs surgery cases, 4.53% ( n = 610) had incidental skin cancers found during removal of the initially identified tumor. Of the 610 cases, 88.4% ( n = 539) had basal cell carcinoma as the primary tumor and either squamous cell carcinoma (SCC) or SCC in situ as the incidental tumor. About 7.87% ( n = 48) had SCC as the primary tumor and basal cell carcinoma as the incidental tumor. All tumors were removed with clear margins and without significant complications.

Conclusion: Diagnosis of incidental tumors during Mohs surgery enables early detection of skin cancer and circumvents the need for additional surgery, likely resulting in decreased morbidity and improved cost-effectiveness.