Test characteristics of high-resolution ultrasound in the preoperative assessment of margins of basal cell and squamous cell carcinoma in patients undergoing mohs micrographic surgery

BACKGROUND: Noninvasive techniques to assess subclinical spread of nonmelanoma skin cancer (NMSC) may improve surgical precision. High-resolution ultrasound has shown promise in evaluating the extent of NMSC. OBJECTIVES: To determine the accuracy of high-resolution ultrasound to assess the margins of basal cell (BCC) and squamous cell carcinomas (SCC) before Mohs micrographic surgery (MMS). METHODS: We enrolled 100 patients with invasive SCC or BCC. Before the first stage of MMS, a Mohs surgeon delineated the intended surgical margin. Subsequently, a trained ultrasound technologist independently evaluated disease extent using the EPISCAN I-200 to evaluate tumor extent beyond this margin. The accuracy of high-resolution ultrasound was subsequently tested by comparison with pathology from frozen sections. RESULTS: The test characteristics of the high-resolution ultrasound were sensitivity=32%, specificity=88%, positive predictive value=47%, and negative predictive value=79%. Subgroup analyses demonstrated better test characteristics for tumors larger than the median (area>1.74 cm²). Qualitative analyses showed that high-resolution ultrasound was less likely to identify extension from tumors with subtle areas of extension, such as small foci of dermal invasion from infiltrative SCC and micronodular BCC. CONCLUSION: High-resolution ultrasound requires additional refinements to improve the preoperative determination of tumor extent before surgical treatment of NMSC.