Immunophenotypes of canine mammary carcinomas.

Introduction: A new classification system of breast tumours is presently used in human pathology and is based on the immunohistochemical characterization of 4 tumour types, namely luminal-like (A and B type), basal-like, and ERB-B2 positive neoplasms. This approach reveals extremely useful in humans in terms of prognosis.In fact, luminal phenotype seems to have a better prognosis than basal and ERB-B2 respectively. In this preliminary study this classification method has been applied to a series of mammary tumours of the female dog with the aim to verify its prognostic value in veterinary medicine. Material and methods: A series of 45 canine mammary carcinomas with a known two-year post-mastectomy follow-up were selected from our database. A panel of the following antibodies was applied: anti-cytokeratines 14, 5/6, oestrogen receptor (ER), progesterone receptor (PR), and ERB-B2. PR and ER nuclear staining and ERB-B2 membranous staining were considered positive when observed in >10% of tumor cells; CK5/6 and CK14 cytoplasmic staining was considered positive when observed in at least one tumor cell. According to the phenotypic expression, the cases were grouped as follows: luminal-like (ER+/-, PR+/-, CK14-, CK5/6-) type A (ERB-B2-), and B (ERB-B2+); basal-like (ER-, PR-, CK14+, CK5/6+, ERB-B2-); ERB-B2 (ER-, PR-, CK14-, CK5/6-, ERB-B2+). Kaplan-Meyer survival curves were estimated and compared by survival analysis. Results: Thirty-five cases showed a luminal pattern (ER+ and PR+) further subgrouped into 13 A type and 22 B type, according to ERB-B2 positive or negative expression. Ten cases revealed a basal phenotype, and no cases were classified as ERB-B2. Survival analysis produced no significant results, even though a clear prognostic distinction was apparent between basal (more favorable) and luminal (less favorable) after 24 months from mastectomy. As for the two luminal groups, A type showed a better prognosis than B type Discussion: Luminal-like A and B types share the same phenotype but differ in ERB-B2 expression considered an important index for prognosis and tumour progression in canine as well as in human breast cancer. In fact, the survival curve indicates a worse prognostic index for luminal B tumours compared to A subtype. The basal group shows a more favorable behaviour than the others, unlike the human models. If the results are confirmed on a larger number of cases, the hypothesis that tumours originating from myoepithelial cells have a low malignant potential will be reinforced in the dog unlike the human.