Orientador: Julio Lopes Sequeira / Banca: Louisiane de Carvalho Nunes / Banca: Alessandre Hataka / Banca: Sheila Canevese Rahal / Banca: Noeme Souza Rocha / Resumo: O presente trabalho teve como objetivo quantificar e avaliar presença dos mastócitos nos diferentes tipos de neoplasias malignas da glândula mamária da cadela. Através de estudo retrospectivo, foi empregado à coloração histoquímica do azul de toluidina, para detecção de mastócitos, e a técnica imunoistoquímica, usando os anticorpos Ki-67 para proliferação celular e a caspase-3 para identificar as células em apoptose. As amostras (n= 102) foram descritas conforme a Classificação Histopatológica para Neoplasia Mamária do Cão e do Gato da Organização Mundial de Saúde. Os animais sem raça definida apresentaram o maior número de casos, e entre os animais com raça definida, a raça Poodle foi a que apresentou o maior número de casos. A idade média das cadelas foi de 8,6 anos. Os tipos morfológicos de neoplasias encontradas foram o carcinoma in situ com 0,98%, carcinoma complexo com 45,09%, carcinoma simples com 35,29%, carcinossarcoma com 10,78% e os tipos especiais de carcinomas que representaram 7,89% dos casos. Os mastócitos estavam presentes no foco neoplásico em 96,08% das amostras. 99% das amostras apresentaram marcação positiva para o anticorpo Ki-67 (MIB-1). Já a imunomarcação pela caspase-3 revelou marcação positiva em 95% dos casos. Foi observada correlação significativa positiva entre o número de mastócitos e o índice de proliferação (Ki-67) (p˂0,05) nos carcinomas do tipo complexo. Os mastócitos mostraram influência na proliferação das células dos carcinomas complexos, contudo, é necessário mais estudos para elucidar o papel destas células no índice de proliferação / Abstract: The presented study aimed to quantify and evaluate the presence or absence of mast cells in different types of malignancies in the mammary gland of the female dogs. For this, it was used the blue toluidine in the histochemical colours with the purpose of detecting mast cells, and immunohistochemical techniques, using the antibodies Ki-67 to the proliferation of the cells and caspase-3 antibody to identify undergoing cells in apoptosis. All samples were put according to the pathological classification for dog's and cat's breast cancer in the World Health Organization. About the racial pattern, it was observed a higher number of cases in animals without breed, and in the animals with breed, the Poodle was the one with the largest number of cases. The average age of the female dogs was 8.6 years old. The morphological types of neoplasm founded were: carcinoma in situ with 0.98% (1/102), complex carcinoma with 45.09% (46/102), simple carcinoma in 35.29% (36/102) carcinosarcom in 10.78% (11/102) and special types of carcinomas that were represented with 7.89% (08/102) of the total number of cases. The mast cells were presented in the neoplasic focus with 96.08% (98/102), and it prevailed in areas where there are lots of human tissues, especially around the vessels. About the immune numbers of samples using the Ki-67 (MIB-1), it was conclude that 99% (101/102) showed positive results. However, using the caspase-3 it was showed positive results in 95% (97/102). About the influence of mast cells in the proliferation of neoplasic cells, it was observed a significant positive correlation between the number of mast cells and the proliferation (Ki-67) for the complex carcinoma (p 0.05). The correlation between death and cells proliferation showed a negative significant relation in spindle cells carcinomas, between the apoptotic number (Caspase-3) and the proliferation number (NORs). How bigger is the number / Doutor