Multiple Primary Tumours in Oral Cancer: Patient Characteristics and Survival Patterns.

BACKGROUND: The development of multiple primary tumours (MPTs) is an important consequence of oral cancer and one of the leading causes of mortality among these patients. This study aimed to identify some of the risk factors for MPT development in oral cancer patients and to examine its impact on survival rates. METHODS: In this retrospective, population-based cohort study, we retrieved administrative data from the Alberta Cancer Registry database for 3549 patients diagnosed with primary oral cancer (POC) between 2005 and 2020. RESULTS: Among these patients, 513 developed MPTs for an overall incidence of 14.5%. The average time interval for development of the first MPT was 4.04 +/- 3.67 years. The proportion of patients with any comorbid conditions was significantly higher in MPT patients compared with non-MPT patients. Advanced age, average income, comorbidities including chronic obstructive pulmonary disease, diabetes and cardiovascular disease, and increased time from diagnosis to treatment were found to be potential risk factors for MPT development. Analysis revealed a sharp decrease in survival rate of oral cancer patients after developing MPTs. Furthermore, age >45 years, body mass index <18.5, synchronous tumours, stage III and IV POC, >2 comorbid conditions and MPT developing in the digestive system were associated with poor disease-specific survival. CONCLUSION: The development of MPTs significantly affects the survival of oral cancer patients. Advanced age, comorbidities and delayed initiation of treatment were identified as key risk factors for MPTs. The poor survival outcomes, particularly in patients with synchronous tumours, advanced-stage primary cancers and specific comorbid conditions, highlight the need for early detection and proactive management strategies to mitigate these risks and improve long-term survival in this population.