A Review of Mammary Gland Neoplasia in the Bitch and Queen

Abstract

Mammary gland tumors are amongst the most common tumors of bitches and queens. About half of all tumors of the bitch arise from mammary glands and from one third to one half of these are malignant, making mammary tumors the most common malignant neoplasm of the bitch. In the queen, tumors arising from mammary tissues are the third most common occurring neoplasms after skin and lympho-hematopoetic tumors. Nearly all mammary gland tumors in cats are malignant. 

Masses involving the ventral abdomen are occasionally not of mammary gland origin. The differential diagnosis includes skin tumors, foreign body reactions, hernias, neoplasms of other tissues, etc. Mastitis should also be considered. Another primary proliferative, but non-neoplastic mammary gland disease that can present as sudden growth of one or more mammary glands in young cats is a benign condition referred to as fibroadenomatous hyperplasia.

The majority of canine and feline mammary gland tumors arise from epithelial cells of either the glands or ducts. These become either benign (adenomas) or malignant (adenocarcinomas or carcinomas) neoplasms. “Mixed” mammary gland tumors are unusual in that they contain both neoplastic epithelial and mesenchymal cells. These occur in the bitch, but rarely in the queen.

Histopathology is the gold standard for tumor identification and characterization. Unfortunately, the nomenclature used by diagnostic pathologists can be complicated. For example, most classification systems include even very rare mammary tumors, which can make them seem overwhelming.

Several different classification schemes have been published that categorize mammary tumors of cats and dogs based on microscopic features. These have proven to very useful for clinicians. Histopathology findings provide important prognostic information and regardless of the classification system used, they divide tumors into those that are likely to behave in a benign manner from those that have features that identify them as malignant “cancers”. Additionally histopathology allows for accurate staging of the neoplasm in a given patient.

Features that significantly affect survival of affected bitches and queens include: anaplastic phenotype of the neoplastic cells, tumor size and evidence of metastasis. [...]