Receptors for oestrogen, progesterone and epidermal growth factor in normal and tumorous canine mammary tissues.

Receptors for oestrogen (ER), progesterone (PR) and epidermal growth factor (EGF-R) are found in normal mammary tissue (NMT) and/or mammary tumours (MT) from all species studied, including dogs. The aims of this study were to define the possible influences of mammary histology, age, location in the mammary chain and of hormonal status and cycle stage in the expression of ER, PR and EGF-R in mammary tissues from healthy dogs and from dogs with MT. Carcinomas that had lost their glandular structure had significantly lower amounts of receptors. NMT either from healthy or affected dogs had significantly higher amounts of ER than MT. PR levels were significantly higher in benign lesions than in NMT. Steroid receptors in NMT from healthy dogs varied significantly with age (older dogs having more ER), location (posterior glands having higher ER concentrations) and cycle stage (the highest ER concentrations being found in the mid-luteal phase and the lowest PR concentrations in the early luteal phase). In NMT from affected dogs, higher steroid receptor concentrations were found in posterior glands; as in healthy dogs, ER concentrations were low in the follicular phase and high in the luteal phase and PR were high in anoestrus. Steroid receptor content in MT did not vary significantly with age, location or cycle stage or with hormonal status, but tended to vary with cycle stage in a manner similar to that found in NMT from the same dogs. In dogs affected with MT and treated with medroxyprogesterone acetate (MPA), NMT had low concentrations of PR but MT from the same dogs had high PR concentrations. EGF-R were found in the majority of the samples (+/- 65% of MT and +/- 85% of NMT) but there was no significant relation between the concentrations and the parameters studied. Nevertheless, EGF-R content was higher in NMT in the proliferative stages (oestrus, early and mid-luteal phase) than in the non-proliferative stages (early pro-oestrus and anoestrus). EGF-R and ER were significantly and positively correlated only in malignant tumours. There is no apparent difference between affected and healthy dogs in the regulation of ER, PR and EGF-R expression in NMT; on the other hand, some differences between NMT and MT are observed in the regulation of PR (for example under the influence of MPA) and in the correlation between EGF-R and ER expression.