Epidemiological analysis of site relationships of synchronous and metachronous multiple primary cancers in the National Cancer Center, Japan, 1962-1996

Background: Multiple primary cancer (MPC) has been recognized as a problem commonly encountered in routine medical practice. A study of MPC is necessary not only to provide insights into the etiology of cancer, but also to provide information for effective medical care by clinical oncologists. Methods: A cohort of 49 751 cancer patients who were admitted to the National Cancer Center Hospital between 1962 and 1996 was used to study the site relationship of MPC. Logistic and Poisson regression analyses using an internal reference group within the cohort were applied for the calculation of the prevalence odds ratio (POR) for site relationships of synchronous MPC and the incidence rate ratio (IRR) for those of metachronous MPC. Results: Three site combinations with elevated risks for both synchronous and metachronous MPCs, eight with elevated risk for synchronous MPC, five with elevated risk for metachronous MPC and six with decreased risk for synchronous MPC were identified with statistical significance. Among them, the increased risk of metachronous stomach cancer following lymphoma and myeoloma (POR = 1.0 and 1.1, P> 0.05; IRR = 2.5, P < 0.05) and the inverse site-correlation of synchronous MPC between [trachea, bronchus and lung] and other sites of the upper aerodigestive tract [lip, oral cavity and pharynx] (POR = 0.5 and 0.3, P< 0.05) and esophagus (POR = 0.7 and 0.3, P< 0.05) have not been reported previously. Conclusions: Our results suggest that interventions for lymphoma and myeloma might affect the development of subsequent stomach cancer and additional etiological factors other than tobacco smoking are associated with the development of cancer in the upper aerodigestive tract.