Breast Cancer Causes Breast cancer is a malignant tumour that develops from the cells of the breast and is one of the most common cancers affecting women. While the exact cause of this cancer has yet to be determined, recent research clearly indicates that there are several risk factors: The following are the most common causes of breast cancer: According to recent research, there is a high incidence in the age group over 50; however, the incidence is very low in the age group under 25.is very important to say that this disease is very aggressive in path patients 50 years old. Another factor to consider is the menstrual cycle, which is more common in women who have a longer menstrual life, meaning menarche occurs earlier and menstruation ends later. Women who drink alcohol have an increased cause of developing breast cancer. Spinsters and married women who never had children, or who have given birth but h...