Vitamin D receptor expression in canine mammary gland and relationship with clinicopathological parameters and progesterone/oestrogen receptors.

The vitamin D receptor (VDR) belongs to the nuclear class II receptor family. VDR is a ligand transcription factor and mediates the actions of calcitriol, the active product of vitamin D synthesis. Nowadays, it is known that the biological actions of calcitriol include the capacity to modulate cancer features, such as proliferation and differentiation, apoptosis, angiogenesis, invasion and metastasis. VDR expression has been demonstrated in human breast cancer and vitamin D has emerged as a promising targeted therapy. We analyse the VDR expression in normal and neoplastic canine mammary tissue samples and its relationship with clinicopathological parameters and progesterone/oestrogens receptors (PR/ER). Expression of VDR, Ki67 (to evaluate the proliferation index, PI), PR and ER was assessed in 50 mammary gland tissue samples from 41 female dogs by immunohistochemistry. VDR-positive staining was found in the nuclei of both myoepithelial and luminal epithelial cell layers. VDR expression was higher in normal mammary tissue (37/37 cases, 100%) then followed by benign tumours (6/15 cases, 40%) and malignant tumours (9/34 cases, 26.5%) (P = .001). Female dogs aged ≥10 years had lower VDR expression compared with dogs younger (P = .017). Relationship between VDR and breed, number of tumours, tumour size, histologic subtype, histologic grade of malignancy, PI and PR and ER expression was not observed. Studies with more samples are necessary to further evaluate the possible role of VDR in the biological behaviour of canine mammary tumours, and to corroborate the possibility to use the dog as model for human breast cancer.