Mammary gland tumors are very common in dogs, cats, and people but are rare in most other species. Tumors occur primarily in older, intact females. The older a dog is when tumors develop, the more likely it is to be malignant. Incidence rates in dogs vary based on regional variations in the practice of ovariectomy. In the United States, where ovariectomy is commonly performed at young ages, mammary tumor rates are lower than in other areas of the world. Dogs ovariectomized before their first heat cycle are very unlikely to develop a mammary tumor, with decreasing protection with each additional heat cycle. For dogs that have had 3 heat cycles, risk of mammary gland neoplasia is the same as for unsprayed females. The caudal glands (4th and 5th) are most often involved, and presentation with multiple masses is common. Histologic morphology and biologic behavior are highly variable, and classification schemes vary. Mammary tumors predominantly arise from epithelial populations, and primary sarcomas are rare. The finding most consistent with metastatic potential is invasion of neoplastic cells into blood or lymphatic vessels within the tumor. Some reports suggest that the benign and malignant tumors are part of a continuum rather than being distinct entities. Canine mammary tumors are useful as models for human breast cancer.
Links to sections in the MVM:
Overview of Mammary Tumors
Metastatic Tumors
References
Zambrano-Estrada X, Landaverde-Quiroz B, Dueñas-Bocanegra AA, et al. Molecular iodine/doxorubicin neoadjuvant treatment impair invasive capacity and attenuate side effect in canine mammary cancer. BMC Vet Res. 2018 Mar 12;14(1):87. doi: 10.1186/s12917-018-1411-6
Feliciano MAR, Ramirez RAU, Maronezi MC, et al. Accuracy of four ultrasonography techniques in predicting histopathological classification of canine mammary carcinomas. Vet Radiol Ultrasound. 2018 Feb 11. doi: 10.1111/vru.12606
Dolka I, Czopowicz M, Gruk-Jurka A, et al. Diagnostic efficacy of smear cytology and Robinson's cytologic grading of canine mammary tumors with respect to histopathology, cytomorphometry, metastases and overall survival. PLoS One. 2018 Jan 23;13(1):e0191595. doi: 10.1371/journal.pone.0191595
Sadhasivan SBM, Shafluzama M, Shammi M, et al. Studies on reconstruction of large skin defects following mammary tumor excision in dogs. Vet World. 2017 Dec;10(12):1521-1528. doi: 10.14202/vetworld.2017.1521-1528
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