Breast cancer: Clinical

Breast cancer, or breast carcinoma, is an uncontrolled growth of epithelial cells within the breast.

It’s the most common cancer in women, but can rarely affect men as well.

Now, estrogen and progesterone stimulate breast cells to grow and divide, and exposure to them over long periods of time increases the risk of breast cancer.

More menstrual cycles over a lifetime means a higher cumulative exposure to these hormones. That’s why factors that increase the number of menstrual cycles increases the risk of breast cancer.

That includes things like early menarche, or a first menstrual bleeding before 11 years of age, and late menopause, after 54 years of age.

On the flip side, some factors that are associated with fewer lifetime menstrual cycles - like pregnancy and a longer time breastfeeding - decrease the risk of breast cancer.

Similarly, hormone replacement therapy used to treat menopause symptoms, also increases that risk.

Another risk factor is exposure to ionizing radiation, like from chest X-rays and CT scans or previous radiation therapy for other cancers located in the chest.

Breast cancer has been linked to mutations in tumor suppressor genes, like BRCA1, BRCA2, and TP53, which normally prevent uncontrolled cell division.

Some breast cancers have mutations in the ERBB2 gene which causes an increase in human epidermal growth factor receptor 2, or HER2, which promotes cell division.

Finally, some breast cancer cells have estrogen or ER receptors and progesterone or PR receptors, which allow them to divide faster in the presence of these hormones.

Breast cancer is the second leading cause of cancer deaths in women after lung cancer, and this is largely due to the fact that breast cancers often don’t cause pain or discomfort until they’ve metastasized.