The impact of clinicopathological factors on clinical outcomes in patients with salivary gland adenoid cystic carcinoma: a multi-institutional analysis in Japan

Background: Owing to the low incidence of adenoid cystic carcinoma (AdCC), reliable survival estimates and prognostic factors remained unclarified. Methods: In this multi-institutional retrospective analysis, we collected 192 AdCC cases, and investigated the impact of clinicopathological factors on clinical outcomes of the patients. All AdCC cases were of salivary gland origin and were surgically treated with curative intent. Diagnoses of AdCC were validated by a central pathology review by expert pathologists. Results: The 5-year overall survival (OS) and disease-free survival (DFS) rates were 92.5 and 50.0%, respectively. Treatment failure occurred in 89 patients (46%) with the distant failures in 65 (34%). Multivariate analysis indicated that pN2 and a pathologically positive surgical margin were independent prognostic factors for both OS and DFS. Histological grade III was an independent prognostic factor for OS. A primary site in the submandibular gland, pT3/4, pN1, and histological grade II were independent prognostic factors for DFS. Postoperative radiation therapy (PORT) improved the locoregional control (LRC) rate. Prophylactic neck dissection was not associated with a better OS or better LRC among patients with cN0. Facial nerve dissection did not improve clinical outcomes in parotid AdCC cases without facial nerve palsy. Conclusions: A higher TN classification, a pathologically positive surgical margin, and a higher histological grade were associated with a lower OS. PORT improved LRC rates but neck dissection failed to improve clinical outcomes in patients with cN0. As the distant metastasis was frequent, effective systemic therapy is imperative to improve the survival of AdCC patients.