Clinical Features of Oral Multiple Primary Carcinomas Compared with Oral Single Primary Carcinoma

[Background] Owing to the increase in the older population and the increased life span, the number of patients with oral multiple primary carcinomas will increase. Predicting the second and third carcinoma clinically is difficult, and the presence of second or third carcinomas is a factor that determines the prognosis of oral carcinoma. In this study, we examined the clinical features of oral multiple primary carcinomas treated in our department. [Methods] We retrospectively reviewed the medical records of patients with oral squamous cell carcinoma who underwent radical treatment at and were followed by the Department of Oral and Maxillofacial Surgery, Tottori University Hospital from January 2003 to October 2017. [Results] This study included 261 patients: 241 patients had oral single primary carcinoma and 20 patients had oral multiple primary carcinomas. Oral multiple primary carcinomas showed female predilection and occurred more frequently in the lower gingiva and significantly less frequently in the tongue (P < 0.01). Oral multiple primary carcinomas showed a significantly higher recurrence rate (P < 0.01). The 5-year overall survival of oral single primary carcinoma patients was 88.0% compared with 95% for oral multiple primary carcinomas, with no significant difference (log rank test, P = 0.54). However, the 15-year survival rate dropped to 28.1% in oral multiple primary carcinomas. The cumulative disease incidence rates of metachronous second primary carcinoma from first carcinoma at 5 years and 10 years were 3.45% and 5.36%, respectively. [Conclusion] Oral multiple primary carcinomas rarely occur in the tongue. The 5-year survival rate showed no difference between single and multiple carcinoma patients, but over longer observation, the prognosis of multiple carcinoma was poor owing to a high recurrence rate. Because of the high recurrence rate and risk of further metachronous carcinoma in oral multiple primary carcinomas, longer-term follow-up is required.