Clinical Value of Paraffin Sections in Association with Mohs Micrographic Surgery for Nonmelanoma Skin Cancers

Background During Mohs micrographic surgery (MMS), situations can arise in which paraffin sections may be used in conjunction with frozen sections. Objective To determine the clinical value of paraffin sections in association with MMS, including frequency, reasons, and information obtained. Methods and Materials Single-center retrospective cohort study at a cancer center. MMS cases for nonmelanoma skin cancers over a 5-year period in which paraffin sections were used were identified. Reasons for submitting paraffin sections were reviewed. Initial biopsy, Mohs frozen section, and paraffin section diagnoses and histologic subtypes were compared. Results In 258 (7.8%) cases, paraffin sections were used in association with MMS. The most common reasons were to further assess high-risk histologic features or unusual frozen section findings, to complete tumor staging of cutaneous squamous cell carcinomas, and to assess perineural invasion (PNI). Initial biopsy diagnosis differed from the Mohs frozen and paraffin section diagnoses in 20% to 22% of cases. The initial biopsy histologic subtype changed from low or indeterminate to high risk in Mohs frozen and paraffin sections in 24% to 29% of cases. Conclusion In MMS for select high-risk or unusual nonmelanoma skin cancers, paraffin sections are useful in more accurately documenting tumor histology, completing cutaneous squamous cell carcinoma staging, and detecting PNI.