The causes of breast cancer remain elusive. Significant risk factors include a family history of breast cancer (mother, sister, grandmother, aunt) and being a woman older than age 45 and premenopausal. Other probable risk factors being investigated include a long menstrual cycle, early onset of menses, or late menopause; first pregnancy after age 31; a high-fat diet; endometrial or ovarian cancer; radiation exposure; estrogen therapy; antihypertensive therapy; alcohol and tobacco use; and preexisting fibrocystic disease. The discovery of the breast cancer gene BRCA1 confirms the theory that the disease can be inherited from either the mother or the father.

About half of all breast cancers develop in the upper outer quadrant, the section containing the most glandular tissue. The second most common cancer site is the nipple, where all the breast ducts converge. The next most common site is the upper inner quadrant, followed by the lower outer quadrant and, finally, the lower inner quadrant.

Growth rates vary. Theoretically, slow-growing breast cancer may take up to 8 years to become palpable at 1 cm. Breast cancer spreads by way of the lymphatic system and the bloodstream through the right side of the heart to the lungs and to the other breast, chest wall, liver, bone, and brain.

The estimated breast cancer growth rate is called its doubling time, or the time it takes malignant cells to double in number. Survival time is based on tumor size and the number of involved lymph nodes.

Classified by histologic appearance and the lesion’s location, breast cancer may be described as:

Coupled with a staging system, these classifications provide a clearer picture of the cancer’s extent. The most common system for staging, before and after surgery, is the tumor, node, metastasis system.

Disease progression and metastasis of breast cancer lead to site-specific complications, including infection, decreased mobility if breast cancer metastasizes to the bone, central nervous system effects if the tumor metastasizes to the brain, and respiratory problems if the disease spreads to the lung.

The patient most often reports that she detected a painless lump or mass in her breast or that she noticed a thickening of breast tissue. Otherwise, the disease most
commonly appears on a mammogram before a lesion becomes palpable. The patient’s health history may indicate several significant risk factors for breast cancer.

Inspection of the patient’s breast may reveal clear, milky, or bloody nipple discharge, nipple retraction, scaly skin around the nipple, and skin changes, such as dimpling, peau d’orange, or inflammation. Arm edema, which is also identified on inspection, may indicate advanced nodal involvement.

Palpation may identify a hard lump, mass, or thickening of breast tissue. Palpation of the cervical supraclavicular and axillary nodes may also disclose lumps or enlargement.