Prognostic histopathological and molecular markers in feline mammary neoplasia

Feline mammary tumours comprise approximately 11% of feline non-integumentary neoplasms, are more commonly malignant than benign, and carry a poor prognosis attributable to a high probability of local recurrence and metastasis. This review discusses histopathological and molecular markers that could aid in prognostic discrimination, and draws comparisons with studies examining prognostic markers in breast cancer. Tumour grade and mitotic index correlate with survival data and could be useful for prognostication. Although assessment of Ki67 expression might have prognostic potential, further studies are required to corroborate the correlation between expression and clinical outcome. Additional molecular markers that have been investigated for prognostic potential can be grouped according to the 'hallmarks of cancer'. Many studies utilise 'surrogate markers' of clinical outcome, such as correlation with histological grade, to assess the prognostic value of molecular markers, and further investigation is therefore necessary before reaching firm conclusions regarding the prognostic value of some markers. Feline mammary tumours have been proposed as spontaneous models of breast cancer but might only be suitable models for certain molecular sub-types. Compared to humans, cats tend to have a high percentage of mammary tumours which are oestrogen receptor-negative and they might therefore be suitable models for late stage oestrogen receptor-negative breast cancer. The basal-like properties of feline mammary carcinomas offer another avenue for future research in this field of comparative oncology.