Incidence and Patterns of Second Primary Malignancies Following Oral Cavity Cancers in a Prevalent Area of Betel-nut Chewing: A Population-based Cohort of 26 166 Patients in Taiwan

Objective: The incidence of oral cavity cancers is increasing rapidly in South-East Asia, which may be attributable to tobacco smoking, alcohol and betel-nut chewing. However, the actual incidence and risk of second primary malignancies after oral cavity cancers have not been well established in this region. A population-based study was therefore conducted. Methods: Standardized incidence ratios and cumulative incidences were calculated for second primary cancers using the Taiwan Cancer Registry database for the period 1979-2003, which included 26 166 cases having an initial diagnosis of oral cavity cancers. Results: A 3.11-fold increase in risk for second cancer at all sites was observed after oral cavity cancers compared with the general population (standardized incidence ratio = 3.11, 95% confidence interval: 2.97-3.25). Of nine sites with excess risks of developing a second cancer, the frequency was highest in the oral/pharynx (60%), followed by lung (7.2%) and esophagus (5.5%). Second esophageal and lung cancers had a greater impact on survival compared with other types of second cancer. Notably, the risk excess was more prominent for patients with a follow-up interval of <= 1 year and a first primary cancer diagnosed at age of <= 40. These patients may justify closer surveillance. Conclusions: This is the largest population-based study with a homogeneous patient population focusing on oral cavity cancers within a high-incidence area. We found that oral cavity cancers are associated with an increased risk of nine second malignancies, which had a negative impact on survival.