Breast cancer is a type of cancer that starts in the cells of the breast. It can affect both men and women, but it is much more common in women. In breast cancer, some of the cells in the breast begin to grow uncontrollably, forming a lump or tumor. These cancerous cells can spread to other parts of the body if not treated. The most common symptoms of breast cancer include a lump in the breast, changes in the size or shape of the breast, or unusual pain. Early detection through screening, like mammograms, can help find breast cancer at an early stage, making it easier to treat.