Inflammatory mammary carcinoma (IMC) is the most aggressive spontaneous type of mammary cancer in both women and dogs. Previous findings indicate that canine IMC could be a source of oestrogens. It has been shown that oestrogens produced in the tumour could act as mitogens and promote tumour growth. A positive correlation between IGF-I and breast cancer risk is reported in women but to date this point is unknown for canine mammary tumours. In order to investigate the possible role of IGF-I and oestrogens in the development of canine IMC, we determined the oestrogen and IGF-I profiles in tissue homogenates of IMC, and then they were compared with mammary dysplasias, benign mammary tumours and other non-IMC malignant mammary tumours.

Eighty-six mammary samples (10 normal mammary tissue (NMG), 21 dysplasias (DYSP), 26 benign (BMT), 22 malignant (MMT) and 7 IMC) from 35 female dogs were used. All tissues were obtained from the Veterinary Teaching Hospital of Madrid and the experimental design was approved by the Ethics Committee. 17β-Oestradiol, SO4E1 and IGF-I were measured by EIA techniques validated for this species. Statistical analysis was done by using Student’s paired t test.

IMC displayed the following oestrogen and IGF-I levels (mean ± S.E.M.): E2, 675.19 ± 33.00 ng g^-1; E1SO4, 2.84 ± 0.32 mg g^-1; IGF-I, 194.40 ± 29.15 ng g^-1. All the values were significantly higher (P < 0.001) when compared with the levels determined for malignant, benign, dysplasias, and normal mammary tissue.

These results point to a role of IGF-I and oestrogens in the suggested autocrine mechanism involved in the development of canine inflammatory carcinoma.