Immunohistochemical Detection of Mdm2 and p53 in Feline Mammary Gland Tumors

Emerging Biomarkers and Targeted Therapies in Feline Mammary Carcinoma

Feline mammary carcinoma (FMC) is a common aggressive malignancy with a low survival rate that lacks viable therapeutic options beyond mastectomy. Recently, increasing efforts have been made to understand the molecular mechanisms underlying FMC development, using the knowledge gained from studies on human breast cancer to discover new diagnostic and prognostic biomarkers, thus reinforcing the utility of the cat as a cancer model. In this article, we review the current knowledge on FMC pathogenesis, biomarkers, and prognosis factors and offer new insights into novel therapeutic options for HER2-positive and triple-negative FMC subtypes.

Felis catus papillomavirus type-2 E6 binds to E6AP, promotes E6AP/p53 binding and enhances p53 proteasomal degradation

E6 from high risk human papillomaviruses (HR HPVs) promotes ubiquitination and degradation of p53 tumour suppressor by mediating its binding to ubiquitin ligase E6AP in a ternary complex, contributing to cell transformation in cervical cancer. We have previously shown that Felis catus papillomavirus type −2 (FcaPV-2) E6 is expressed in feline squamous cell carcinoma (SCC) and displays the ability to bind p53 and decrease its protein levels in transfected CRFK cells. However, the mechanism of p53 downregulation has not yet been characterized. Here we show that FcaPV-2 E6 bound to E6AP, which in turn was bound by p53 exclusively in cells expressing the viral oncoprotein (CRFKE6). Furthermore, p53 was highly poly-ubiquitinated and underwent accumulation upon E6AP gene knockdown in CRFKE6. Half-life experiments and proteasome inhibition treatments indicated that down-regulation of p53 protein in CRFKE6 was due to accelerated proteasomal degradation. E6AP/p53 binding was also demonstrated in two feline SCC cell lines expressing FcaPV-2 E6, where p53 protein levels and poly-ubiquitination degree were proportional to E6 mRNA levels. The data obtained in both artificial and spontaneous in vitro models suggest that FcaPV-2 E6 degrades p53 through a molecular mechanism similar to HR HPVs, possibly contributing to the development of feline SCC.

Prognostic evaluation of feline mammary carcinomas: a review of the literature

A large number of studies have investigated feline mammary tumors in an attempt to identify prognostic markers and generate comparative analyses with human breast cancer. Nevertheless, a retrospective base of assessments and the lack of standardization in methodology and study design have caused weakness in study results, making comparison difficult. We examined feline mammary tumor publications and evaluated postulated prognostic parameters according to the recently published "Recommended Guidelines for the Conduct and Evaluation of Prognostic Studies in Veterinary Oncology." Using these criteria, we determined with statistically significant reliability that prognostic parameters for feline mammary tumors are tumor grading and lymph node/lymphovascular invasion. Furthermore, tumor subtype, size, and staging are worthy of further standardized investigation. We present statistical significance for each studied parameter as well as its relevance to disease progression and survival. Our evaluation suggests that marker expression (ie, Ki67, HER2, ER) may provide relevant information applicable for therapeutic predictions; however, consensus efforts and protocol standardization are needed. We identify and discuss major points of concern--such as sample preservation and selection, standardization of immunohistochemical protocols, and evaluation of results--to provide support for subsequent reliable analyses.

Early detection, aggressive therapy: optimizing the management of feline mammary masses

AIMS

This article reviews the incidence, etiology, diagnosis, treatment and prognosis of mammary tumors in cats.

PRACTICAL RELEVANCE

Approximately 80% of feline mammary masses are malignant, with adenocarcinoma being the most common tumor type. Early diagnosis is, therefore, essential to improve the prognosis and quality of life of affected cats.

TREATMENT APPROACHES

Surgery is the most widely used treatment for malignant tumors. However, as mammary tumors are often advanced and metastasis has already occurred by the time of diagnosis, surgery routinely does not provide a cure. Ovariohysterectomy or hormonal therapy are the treatments of choice for fibroadenomatous hyperplasia (the most common benign mass) and usually lead to a successful outcome.