Carcinoma of the parotid Gland: A Population-Based study of incidence and treatment outcomes in 1018 patients

INTRO: Population-based studies predominantly focused on carcinoma of the parotid gland (CPG) are rare. The study aims were to analyze the incidence of CPG and to assess treatment outcomes in relation to histopathology, preoperative diagnosis and adjuvant radiotherapy. METHODS: A retrospective analysis was conducted on data from the Swedish Head and Neck Cancer Register (SweHNCR), including 1,018 patients diagnosed with CPG between 2008 and 2019. RESULTS: The age-adjusted incidence remained stable with a mean of 0.9 (range 0.65-1.08) cases per 100,000 person-years (ASR-Europe). Curative treatment was administered to 90 % of the patients, with a recurrence rate of 9 % within 3 years. The highest recurrence rates were observed in patients with salivary duct carcinoma and adenocarcinoma, while patients with acinic cell and mucoepidermoid carcinomas had lower recurrence rates. For stage I-II tumors, the 5-year relative survival was unaffected by whether the malignant diagnosis was known preoperatively. Male sex, increasing age, stage III-IV disease, and a World Health Organization/ Eastern Cooperative Oncology Group (WHO/ECOG) performance status 2-4 was independently associated with increased overall mortality risk, whereas the timing of adjuvant radiotherapy was not. CONCLUSION: This study contributes to establishing the incidence and treatment outcomes of CPG in Sweden and highlights the diverse histopathological diagnoses of these tumors. Notably, unknown malignancy at the time of surgery did not impact survival in early-stage disease, and the timing of postoperative radiotherapy was not associated with overall survival.