Metastatic Sites in Rare Genitourinary Malignancies and Primary Cancer Sites in Genitourinary Organ Metastases: A Secondary Analysis Using the Japanese Pathological Autopsy Registry Database.

Background: The epidemiology of metastases from rare genitourinary cancer and metastases to genitourinary organs from other primary neoplasms remains poorly understood. Objective: To investigate the epidemiology of rare genitourinary metastases from rare genitourinary organ-type cancer and to genitourinary organs using data from a large national autopsy registry in Japan. Design setting and participants: A secondary analysis of the data reported in the Annual of the Pathological Autopsy Cases in Japan and the Japanese Mortality Database from 1993 to 2020 was performed. Outcome measurements and statistical analysis: Via a retrospective epidemiologic analysis, we evaluated the frequency (probability of occurrence [number per person]) and proportion (percentage) of metastases from upper urinary tract, adrenal, testicular, urethral, and penile cancers. Moreover, the sites of primary tumors metastasizing to genitourinary organs were examined. Results and limitations: In Japan, the mortality rate of upper urinary tract cancer is increasing rapidly. In the integrated database with 365 099 autopsies and 835 959 metastatic organs, the major metastatic sites (range of frequency ratios) of rare genitourinary organ-type cancers were the lungs (0.38-0.47), liver (0.21-0.56), bone (0.16-0.33), adrenal gland (0.10-0.20), peritoneum (0.0-0.16), and kidneys (0.07-0.22). The major primary sites (range of proportions) of genitourinary organ metastases were the respiratory tract (5.6-34.0%), stomach (4.7-27.0%), hematologic site (0.9-24.9%), lymphoid (2.4-22.2%), bladder (0.8-20.0%), prostate (0.7-14.1%), rectal (2.0-11.7%), and pancreas (2.6-11.0%). The cancers with a high likelihood of genitourinary metastasis were respiratory and stomach cancers. However, the study lacked individual-level information, and there might be a concomitant selection bias in this autopsy study. Conclusions: This large-scale autopsy database analysis identified the epidemiology of metastasis from rare genitourinary organ-type cancer and the origins of metastasis to genitourinary organs. Patient summary: This study provides valuable metastatic epidemiologic data and clinical information that are fundamental to the mechanisms of genitourinary metastasis.