CTLA4 and breast carcinoma: However, a recent study reported a positive correlation between higher HER2 mRNA levels and better clinical outcome in feline mammary carcinoma25, while a study using a mouse model of HER2 positive breast cancer found that induced intratumoral expression of a CTLA-4 monoclonal antibody not only failed to exert anti-tumor effects, but instead stimulated tumor growth26, in support of our results.