In my opinion, cytology has virtually no place in the investigation of mammary enlargement in dogs or cats. Cytology cannot determine prognosis since it cannot reliably distinguish behaviorally benign from behaviorally malignant mammary neoplasia in either species. Many tumors have a lot of inflammation within them, and mammary gland with inflammatory disease will have dysplastic changes easily mistaken for neoplasia. There is too much regional variation in the presence or absence of predictors of malignancy to justify the use of tru cut biopsies. When it comes to mammary masses, full excisional biopsies are still the rule . . . for good reason.

There may be some very special circumstances in which cytology or tru cut samples is justifiable. For example, is the enlarged inguinal nodule adjacent to a mammary tumor another tumor, a reactive lymph node, or lymph node with metastasis? Is a mammary lump in a dog with multiple mast cell tumors another mast cell tumor, or is it an independent mammary tumor? Is the lump recurring along my suture line some kind of postoperative inflammation, or is it a recurring tumor?