Incidence of Multiple Primary Cancer in Taiwan - A population-based cancer registration Study

Introduction: The advances in cancer diagnosis and treatment have allowed for more effective cancer care and prolonged patient survival. However, clinical oncologists are also aware of the increased incidence of multiple primary cancers (MPC) followinga patient's first cancer. Due to genetic susceptibility, carcinogenic exposure, and treatment effects, patients who have been diagnosed with cancer are more likely to develop MPC in their lifetime. The present study analyzed the relative risk of developing MPC for the top 10 leading cancers in Taiwan.

Method: All newly diagnosed cases of invasive cancer belonging to the top 10 leading cancers and reported to the Taiwan Cancer Registry database between 1996 and 2005 were selected for this study. MPC was defined as a separate diagnosis of independent cancer two months after the first cancer was diagnosed. The standardized incidence ratio (SIR) was calculated as the number of MPC observed divided by the expected number of general population for each 5-year period, adjusted by age and gender.

Result: A total of 223635 male and 173649 female patients were included. They had been followed for 735119 and 840613 person years during which 11781 (5.3%) and 6294 (3.6%) MPCs were diagnosed, respectively. Most cancers had a significantly high SIR (ranging from 1.10-4.42), except Stomach for women and liver, lung and prostate for men. Elevated SIRs were found for Oral cavity, Esophagus, Nasopharynx and Lung cancers for male patients, and Breast, Corpus Uteri and Ovary cancers for female patients.

Conclusion: For some specific primary cancers, continuous medical management is required following the initial treatment.