Topographic Correlation of Histopathological Subtypes in Canine Mammary Tumors: Evidence of Non-Random Tumor Distribution

Abstract

Canine mammary tumors (CMTs) are among the most frequently diagnosed neoplasms in female dogs, with complex etiologies involving age, breed, body size, and reproductive status. This retrospective study analyzed 250 cases comprising 361 mammary tumors to evaluate demographic patterns, histopathological subtypes, and their topographical distribution. The majority of tumors (88.64%) were malignant, with complex carcinoma being the most common subtype (24%), followed by intraductal papillary carcinoma (14.95%). The mean age at diagnosis was 9.36 years, with 60.8% of cases occurring in dogs older than 8 years. Mixed-breed dogs were most frequently affected, followed by Bichon-type breeds and German Shepherds. Small-sized dogs (<10 kg) accounted for 43.5% of cases. Regarding the reproductive status, 35.6% of dogs were unspayed, while the remainder were either intact or had an undetermined status, reflecting regional spaying practices. A statistically significant association was identified between histological subtype and mammary gland location, revealing non-random, region-specific tumor distribution. Complex carcinomas were frequently located in the left canial abdominal mammary segment (L.A2), right canial abdominal mammary segment (R.A2), and left inguinal mammary segment (L.ING); mixed and tubular carcinomas were more prevalent in R.A2 and R.ING; and tubulopapillary carcinomas appeared predominantly in L.ING. While no significant overall association was found between tumor grade and gland location, grade III carcinomas showed a possible predilection for the left inguinal gland (L.INGH), indicating a regional tendency that warrants further investigation. These findings underscore the importance of anatomical factors in the development of CMTs and support the integration of gland-specific tumor patterns into diagnostic assessment and surgical decision-making.