Epidemiological analysis of mammary tumors in female dogs in Japan: A study based on Kyushu-Okinawa region.

Canine mammary tumors (CMTs) are common tumors in female dogs (FDs), and at least nearly half of these lesions of malignant. We examined the epidemiology of CMTs in Japan using excisional biopsy cases (n = 7802) collected from 2005 to 2023 in the Kyushu-Okinawa region. We investigated the prevalence, effects of breed, neutering, and age on CMT and malignant CMT (mCMT) risk through general statistics and multivariate analyses. The distribution of CMT histological types was also compared among different breeds and mixed breeds. In the Cohort (n = 6197) consisting of cases from primary veterinary hospitals, the numbers of CMT and mCMT cases (2928 and 822 cases, respectively) and the adjusted prevalence is ranged 4.76-8.09 per 1000 dogs and increasing over time (P < 0.001). A multivariate model identified breeds with high or low risks of CMT or mCMT. Neutered FDs had lower risk of CMT than intact FDs (risk ratio = 0.57, 95 %CI: 0.53-0.61). Compared to the age with the highest incidence, those aged ≥ 8 and ≥ 14 years had comparable rates of CMT and mCMT, respectively. Certain breeds exhibited biases regarding CMT histological types compared to mixed breeds. This first epidemiological analysis of CMT in Japan will be a valuable resource for CMT control.