Immunology and mammary cancer development: addressing the role of mast cells

Background: Mammary cancer is one of the most frequent cancers worldwide. Mast cells are among the cells of tumor microenvironment and have been associated with increased angiogenesis and poor prognosis. Despite this, the role of mast cells on mammary cancer is not fully elucidated. In this way, this work studied the role of mast cells in a rat model of mammary cancer chemically-induced. Material and methods: All experiments were performed in accordance with the Portuguese and European legislation on the protection of animals used for scientific purposes. The experiments were approved by the Portuguese (no.008961) and University (CE_12-2013) Ethics Committees. Thirty-four female Sprague-Dawley rats were randomly divided into five experimental groups. At seven weeks of age, mammary tumors’ development was induced in animals from groups I, II, III (n=10+10+10) by a single intraperitoneal injection of the carcinogen N-methyl-N-nitrosourea (MNU). Groups II and IV (n=2) were treated with ketotifen in drinking water (1 mg/kg/day, 7 days/week) immediately after the MNU administration for 18 weeks, while the group III received the ketotifen after the development of the first mammary tumor. Groups I and V (n=2) received only water. Animals were sacrificed at 25 weeks of age by an overdose of ketamine and xylazine, followed by an exsanguination by cardiac puncture. Mammary tumors were collected and immersed in formalin for posterior analysis. Tumors’ vascularization, proliferation and apoptosis were also assessed by immunohistochemistry (Vascular Endothelial Growth Factor (VEGF)-A, Ki-67, and caspases-3 and -9). Results: Animals from groups IV and V did not develop any mammary tumor. Twenty-one animals (six animals from group I, eight animals from group II and seven animals from group III) developed a total of 58 mammary tumors, mainly classified as papillary non-invasive carcinomas. Tumors’ vascularization was similar among groups (p>0.05). Mammary tumors from group II exhibited the lowest proliferation (p