Abstract:

Background and purpose: Salivary duct carcinoma (SDC) is a group of rare and highly heterogeneous diseases. It predominantly arises in the parotid glands of middle-aged and elderly males, with high rates of recurrence and metastasis, as well as a poor prognosis. Currently, there is a lack of clinical data on SDC. This study aimed to evaluate the clinical characteristics of SDC patients and explore high-risk factors affecting prognosis, so as to provide clinical references for physicians. Methods: Clinical data of patients with primary SDC who were admitted to Tianjin Medical University Cancer Institute and Hospital and Tianjin Stomatological Hospital Affiliated to Nankai University School of Medicine from 2012 to 2024, were collected retrospectively. Inclusion criteria: ① patients diagnosed with primary SDC; ② availability of American Joint Committee on Cancer (AJCC) staging data. Exclusion criteria: ① concurrent other malignant tumors; ② incomplete or missing medical records; ③ death due to non-SDC causes; ④ duplicate cases from the two participating hospitals. Data retrieved encompassed epidemiological information (gender, age) and clinical details (time of diagnosis, tumor characteristics, treatment regimen, recurrence and metastasis status, and pathological data). Survival analysis was performed using the Kaplan-Meier method, and factors related to prognosis were explored through univariate COX proportional hazards regression model analysis. This study was approved by the Ethics Committee of Tianjin Stomatological Hospital Affiliated to Nankai University School of Medicine (ethics number: PH2023-B-016), and patient informed consent was waived. Results: A total of 87 patients with primary SDC were included in this study, among whom 77% were male, 69% had primary lesions in the parotid gland, 29.9% in the submandibular gland, and one patient had a primary lesion in the minor salivary gland of the nasal cavity. 49.3% of the patients had concurrent cervical lymph node metastasis. The median overall survival (OS) of the entire group was 31.2 months, the median progression-free survival (PFS) was 20.3 months, and the 5-year OS rate was 52.6%. The 5-year OS rate for tumors originating from the parotid gland was 60%, which was better than the 32.9% for those originating from the submandibular gland. Among the 85 patients who received surgical treatment, 65.9% underwent both resection of the primary tumor and neck dissection. Postoperative radiotherapy was administered to 49 patients. During the follow-up period, 46% of the patients developed recurrence or metastasis, with lung and bone metastases being the most common. The median OS and local progression-free time in the postoperative radiotherapy group were significantly longer compared with those in the group without radiotherapy, however, the difference was not statistically significant. Conclusion: SDC is a malignant and aggressive disease that predominantly occurs in the parotid glands of middle-aged and elderly males, with a high rate of lymph node metastasis and poor prognosis. Clinically, it is recommended that patients with SDC undergo radical resection of the primary lesion and cervical lymph node dissection, combined with postoperative adjuvant radiotherapy. Targeted therapy and immunotherapy are worthy of further exploration.

Key words: Salivary duct carcinoma, Cervical lymph node dissection, Radiotherapy, Recurrence, Metastasis, Prognosis