Predictors of Distant Metastasis and Survival in Adenoid Cystic Carcinoma of the External Auditory Canal

OBJECTIVE: To analyze the predictors of both distant metastasis and survival in patients with adenoid cystic carcinoma of the external auditory canal. STUDY DESIGN: Retrospective patient review. SETTING: A single university hospital. PATIENTS: Eighty-two cases with adenoid cystic carcinoma of the external auditory canal were referred to our institution between 2004 and 2016. MAIN OUTCOME MEASURES: Distant metastasis was detected by lung computed tomography, proton emission tomography computed tomography, or histopathologic examination of tissue samples. Distant metastasis predictors were analyzed using Student's t tests and chi tests. The log-rank tests of Kaplan-Meier survival curves were used to evaluate survival differences. RESULTS: During a median follow-up of 36 months (range, 6-162 mo), distant metastasis developed in 25 patients. The occurrence of distant metastasis was significantly associated with histopathologic subtype, T classification, and local recurrence (p < 0.05). The 1-, 10-, 20-, and 25-year cumulative survival rates in the patents with DM were 95.7, 95.7, 71.7, and 0%, respectively, and all survival rates were 100% for the 57 patients without distant metastasis (p = 0.115). Median survival time after occurrence of distant metastasis was 13 months (range, 1-120 mo). Prognosis was better with solely lung metastasis than with metastases to other visceral organs or bone (p < 0.05). CONCLUSIONS: Distant metastasis appeared to result in a poorer prognosis, occurrence of distant metastasis was significantly associated with local recurrence, extensive surgery is recommended to achieve local control and reduce distant metastasis risk. Routine follow-up investigations for detecting distant metastasis are warranted for patients with an increased risk for distant metastasis.