BackgroundMammary tumors represent the most common neoplastic disease in female dogs. Recently, the promoting role of prolactin (PRL) in the development of human breast carcinoma has been shown. Possible proliferative, anti-apoptotic, migratory and angiogenic effects of PRL on human mammary cancer cells in vitro and in vivo were suggested. The effects of PRL are mediated by its receptor, and alterations in receptor expression are likely to play a role in tumor development. Currently, not much data is available about prolactin receptor (PRLR) expression in canine mammary tumors. To set the basis for investigations on the role of PRL in mammary tumorigenesis in this species, prolactin receptor expression was evaluated by semi-quantitative real time PCR and immunohistochemistry on 10 formalin-fixed, paraffin-embedded samples each of canine non-neoplastic mammary tissue, mammary adenomas and adenocarcinomas.ResultsThe highest PRLR expression levels were found in normal mammary tissue, while adenomas, and to an even higher degree adenocarcinomas, showed a significant decrease in prolactin receptor expression. Compared to normal tissue, PRLR mRNA was reduced 2.4 fold (p = 0.0261) in adenomas and 4.8 fold (p = 0.008) in adenocarcinomas. PRLR mRNA expression was significantly lower in malignant than in benign lesions (p = 0.0165). Immunohistochemistry demonstrated PRLR expression in all three tissue types with signals mostly limited to epithelial cells.ConclusionsMalignant transformation of mammary tissue was associated with a decline in prolactin receptor expression. Further studies are warranted to address the functional significance of this finding.

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20-MHz B-scan high-resolution sonography permits non-invasive, two-dimensional visualisation of micromorphological structures in vivo, and allows precise measurement of the depth and extent of inflammatory skin lesions. In 50 patients, the reactions following intradermal application of 8 recall antigens to the volar forearm were evaluated clinically and sonographically at various times (0, 24, 48, 72 h). In 30 patients, one of the inflammatory papules was excised after 48 h for complete histological work-up (serial sections) and subsequent comparison with the sonographic image. Infiltrates were characterised in the ultrasound scans by the almost regular occurrence of convexity of the skin surface, by a loosened structure (loss of echogenicity) of the corium and by protrusion of the corium into the subcutaneous fatty tissue. It was also possible to follow the dynamics of the type IV reaction with the measurement of echogenicity (densitometry). High-frequency ultrasound is an objective, exact and very sensitive tool for the measurement of type IV reactions after intradermal application of recall antigens and therefore superior to clinical evaluation. The B-scan was superior to the A-scan. However, for routine evaluation of tuberculin-like reactions, sonography is too time-consuming. Our results suggest that densitometry provides no additional or necessary information compared to sonometry.

Mammary tumours represent the most common neoplastic disease of the female dog, and the incidence in female dogs is much higher than in women. Whereas the influence of sexual steroids on breast cancer (BC) development in dogs has been studied, very little is known about the role of prolactin (PRL). New studies show that until recently, the importance of PRL in human BC development and progression has been highly underestimated. PRL plays a role in promoting benign as well as malignant neoplastic cell growth in BC in vitro and in vivo. Sporadic publications proposed a tumour promotor role in the dog. The goal of this review is to summarize our knowledge about PRL and human BC as well as canine mammary tumourigenesis, and propose future research in this area.

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