Impact of Positive-Margin Resection of External Auditory Canal Squamous Cell Carcinoma

SIMPLE SUMMARY: Squamous cell carcinoma of the external auditory canal (EAC-SCC) is sporadic. Its rarity has impeded the collection of evidence from both clinical and basic research, which has delayed the establishment of a standard treatment guideline. It has been considered that negative-margin resection offers the best prognosis. On the other hand, positive-margin resection is still a major cause of recurrence. However, to date, no research has focused on cases with positive-margin resection or specifically assessed the clinical impact of positive-margin resection of EAC-SCC. Our study emphasizes the importance of achieving a negative-margin resection, and we would provide impetus for elucidating the mechanisms of treatment resistance in cases of positive-margin resection. ABSTRACT: Background: Positive-margin resection of external auditory canal squamous cell carcinoma (EAC-SCC) is still a major cause of recurrence. The aim of this study is to examine the clinical impact of positive-margin resection of EAC-SCCs. Methods: We retrospectively reviewed 40 surgical cases with en bloc temporal bone resection of EAC-SCC at a tertiary referral center from October 2016 to March 2022. Results: Two-year disease-specific, overall, and disease-free survival rates for all 40 cases reviewed were 85.2%, 88.85%, and 76.96%, respectively. En bloc resection with a negative margin significantly improved patient prognosis (p < 0.001). Positive-margin resection was observed in 9/40 cases (22.5%). Insufficient assessment of preoperative images was the cause in two of these cases. Postoperative lymph node metastasis and distant metastasis were observed in cases in which vascular, lymphatic duct or perineural invasion was found on postoperative pathological examination. In addition, three cases in which no vascular, lymphatic duct, or perineural invasion was found exhibited local recurrence during the follow-up period. Of the nine positive-margin resection cases, only two showed no postoperative recurrence. Conclusions: Once positive-margin resections are confirmed, cases might have a high risk of tumor recurrence, even with the addition of postoperative adjuvant chemoradiotherapy.