Prolactin and growth hormone immunoactivity in canine mammary adenomas and adenocarcinomas

It is now widely accepted in human medicine that prolactin (PRL) and growth hormone (GH) function in the mammary gland in an autocrine and paracrine manner in tumour formation. The aim of this study was to compare PRL and GH immunoactivity in canine mammary tumours submitted for histopathologic evaluation. Formalin-fixed specimens from spontaneously occurring mammary adenomas and adenocarcinomas from 24 female client-owned dogs were used. Information pertaining to the reproductive status of the patient at the time of mammary tumour diagnosis was obtained from each of the submitting veterinarians. Tissues were paraffin-embedded and sectioned (5 μm) onto charged slides. All slides were deparaffinized and rehydrated. Endogenous peroxidase activity was inactivated with 3% H₂ O_2, and non-specific binding was blocked. Polyclonal rabbit antihuman PRL (DAKO A0569) and GH antibody (DAKO A0570) were applied at a 1:250 and 1:200 dilutions, respectively. A universal rabbit negative control (DAKO N1699) was used. Slides were then reacted with anti-rabbit horseradish peroxidase followed by Nova Red Peroxidase substrate. Slides were counter-stained with haematoxylin, dehydrated and mounted. Tumour type and reproductive status at time of tumour diagnosis were compared individually between tumours that were negative or positive for PRL and GH using a two-tailed analysis of variance. Significance was defined as p < .05. There was no significant relationship between tumour type and PRL and GH presence. In addition, reproductive status at the time of tumour removal was found to be not significant. These results vary from previous reports in canine mammary tumours and warrant further investigation.