Advances in cancer treatment have improved the survival of patients with cancer, with a concomitant increase in the proportion of patients with metastatic brain tumors (MBTs). In this study, we used cancer registries established in Japan after 2016 and available patient data by organ in order to conduct an accurate epidemiological study. To the best of our knowledge, this is the first study to report on the detailed epidemiological data on MBT at the prefectural level in Japan using the Miyazaki Brain Tumor Database and Miyazaki Cancer Registry. This study included 425 new cases of MBTs diagnosed in Miyazaki Prefecture from 2007 to 2016. As per our findings, the most frequent primary tumor in Miyazaki Prefecture was found to be in the lung (49.4%), followed by colon/rectum/anus (9.4%) and breast (8.5%). Among patients with MBTs, 59.1% were males, a number closely similar to that of Japan, as shown in the Japanese Brain Tumor Registry (55.5%). The median age at diagnosis was 68 and 63 years in Miyazaki Prefecture and Japan, respectively. Although more patients were symptomatic in Miyazaki Prefecture than in Japan (88.5% vs. 15.5%), fewer patients opted for surgery (33.6% vs. 61.9%), probably because of their advanced age at diagnosis. As per the findings of this study, the annual incidence rate of new MBTs (i.e., ratio of the number of new cancer registrations to that of new MBT patients in Miyazaki Prefecture) was at 0.41%. The number of tumor sites in MBTs was independent of the total number of cancers per organ. Considering the expansion of cancer registries worldwide, including those on brain tumors, further epidemiological analysis of MBTs is deemed warranted.
Keywords: epidemiology; incidence; metastatic brain tumor.