Abstract

Background Intraepithelial Lesions (IELs) are focal outgrowths of the Mammary Gland (MG), some of which are considered early precursors of tumors. The early detection of IELs has improved the survival rate in women. IELs in female canines have been proposed as a comparative model of IELs in humans. Objective The main aim of this work was to histologically characterize IELs in the MGs of intact female dogs with no signs of mammary disease. Methods Biopsies of the right inguinal MG were obtained from 37 dogs under anesthesia, and the MGs from another 13 female dogs were collected at necropsy (108 total samples). Results MG samples obtained via biopsy did not show any IELs. Among the MGs collected at necropsy, 19 (6/13 dogs) had IELs. The most frequent IELs were adenosis (14 MGs from 4 dogs) and Carcinoma In Situ (CIS) (12 MGs from 3 dogs). Based on the results, we propose that benign and malignant complex lesions be included as IELs in canines. A main finding was that CIS appears to arise spontaneously in multiple lobes/lobules without any evidence of atypical IELs, that is, CIS lesions were malignant from the onset and did not appear to require any other IEL as a precursor. Conclusion: This study demonstrates that female dogs with healthy mammary glands from Bogota have a high rate of IELs in their MGs and that many of the IELs have a malignant character from the onset. Our findings support a new hypothesis for mammary gland carcinogenesis in dogs in accordance with recent theories of the origin of breast carcinomas in humans, i.e., the theory of the Sick Lobe (SL) and biological timing, highlighting the similarities between these pathologies in both species. The importance of myoepithelial cells in the early evolution of IELs is also highlighted in the present work.

Authors and Affiliations