Objective: We hypothesized that moderate exercise in Treadmill may affect the mammary tumor development. N-methyl-N-nitrosourea (MNU) is a commonly used carcinogen to induce mammary carcinomas. The aim of this study was to evaluate the influence of Treadmill exercise in the development (number and weight) of female rat mammary tumors. Method: In this experimental protocol were used 21 female Sprague-Dawley rats. MNU was intraperitoneally administered at 50 days of age in a dose of 50 mg/Kg. Animals were randomly divided in two groups: sedentary (n=11) and exercised (n=10). The exercise program was started after carcinogen administration. Animals were exercised in a Treadmill Control LE8710® after an initial period of familiarization. Thirty-six weeks after MNU administration animals were sacrificed and tumors were counted and weighted. Results: Sedentary and exercised group presented 25 and 20 tumors, respectively. Pearson Chi-Square value was not significant (p>0.05). The mean tumors weight of sedentary group (5.34±10.58 g) was lower than exercised group (8.64 ±13.01 g). The difference between groups was not significant (p>0.05). Conclusion: We observed that exercised group showed minor number of tumors, however the lesions presented higher volume. Future morphological and biochemical analysis of tumors will allow a better understanding of the relation between mammary cancer and physical exercise. Objective: Primary non-Hodgkin's lymphomas is an uncommon disease representing approximately 0.15 % of all reported malignant mammary neoplasms. Clinically they are mainly observed as solitary lesions but may also be seen as multiple foci. Herein, we present a very rare case with the diagnosis of multifocal malignant lymphoma of the breast with a detailed clinicopathologic evaluation. Method: A 56-year-old-female patient with a right palpable breast lump admitted to the hospital. Mammography and ultrasonography findings showed 2 different foci of hypoechoic solid mass forming lesion in the right breast. Excisional biopsy has been performed. Results: In the histopathological evaluation, both lesions demonstrated diffuse infiltration of mammarian tissue with foci of necrosis; mitotically active tumor cells with large nucleus and prominent nucleoli. The immunohistochemical analysis revealed diffuse and strong LCA, CD20, CD43, focal CD68 positivity while pancytokeratin, EMA, CD34, SMA were negative. The case was diagnosed as Diffuse Large B-cell Lymphoma. Conclusion: Breast is an uncommon site for primary malignant lymphomas. We report a very rare case with a diagnosis of multifocal primary non-Hodgkin's lymphoma of the breast.