Fibroadenomatous Hyperplasia (Mammary fibroadenomatosis hyperplasia, MFH) is one of the most common mammary gland conditions diagnosed in young female cats undergoing hormonal contraception. This disease is classified as a benign, hormone-dependent proliferation of the glandular tissue of the mammary gland and its stroma. Clinically, it presents as a pronounced swelling of both mammary chains. Two cases of mammary fibroepithelial hyperplasia (MFH) were reported, one occurring spontaneously and the other following treatment with medroxyprogesterone. Both animals exhibited clinical signs of localized inflammation. Notably, serum amyloid A (SAA) concentrations and white blood cell (WBC) counts were markedly elevated, indicating a systemic inflammatory response. Treatment with the progesterone receptor antagonist aglepristone resulted in complete clinical recovery in both cases. Full remission of clinical signs was achieved approximately four weeks after treatment initiation. Moreover, both SAA levels and WBC counts were normalized by day 14. These findings confirm the efficacy of aglepristone in managing MFH and underscore the utility of monitoring SAA and WBC as markers of inflammation during therapy.