Objectives: The purpose of this study was to compare risk and prognostic factors of invasive breast cancer in two Argentine populations. Patients and Methods: a total of 625 women with invasive breast cancer at different stages were studied: 270 patients from the city of La Plata, and 355 patients from the city of Neuquén. Demographic features and reproductive history were considered as risk factors, while prognostic factors included histopathological data. Statistical analysis was performed. Results: The age at diagnosis was significantly lower in Neuquén than in La Plata; stage III was observed in La Plata at a mean age of 49 years versus 54 years in Neuquén; cutaneous and/or thoracic wall invasion was found at diagnosis in Neuquén, while it was absent in all La Plata patients. Tumor size versus age showed a negative statistical significant relationship; the percentage of HER2/neu-positives in Neuquén was significantly higher than in La Plata, while estrogen/progesterone receptor status showed the contrary. Histological and nuclear grades in Neuquén compared to La Plata were significantly higher, while vascular invasion showed the converse. Considering the number of children, significant differences between groups were found, and also, patients who had breastfed presented a lower number of metastatic lymph nodes than those who had not. Conclusions: La Plata and Neuquén constitute two different populations. The factors that contribute to dividing the groups could be related to the malignant histological characteristics of the tumors, but also the length of breastfeeding and number of children could play a role.