[Clinical features of multiple primary cancers including prostate cancer]

We analyzed the clinical features of multiple primary cancers (MPCs) that included prostate cancer. MPCs were observed in 93 (15.2%) of the patients suffering from prostate cancer. In the MPC group, the organ most commonly involved was the stomach, followed by bladder, colon and lungs. The median age at diagnosis of the first, second and third cancers was 72, 74, and 75 years old, respectively, and the duration between the first and second cancers (median: 20 months) was longer than that between the second and third cancers (median: 8 months). In the 37 MPC patients whose cause of death was obvious, 29 (78.4%) died of a cancer; prostate cancer was not so common (6 patients) as the cause of death. Age at diagnosis and grade distribution of prostate cancer were not significantly different between the MPC and single primary cancer (SPC) groups. However, the proportion of earlier stage was significantly (p < 0.01) higher in the MPC group than in the SPC group, and this trend was more obvious in patients whose prostate cancer was diagnosed as the second cancer. The prostate cancer-specific survival rates were significantly higher in the patients with MPC, and this trend was more obvious in the patients with stage D or moderately differentiated cancer. It is important in the follow up of prostate cancer patients to be aware of the possibility of the occurrence of a second cancer.