Common benign breast diseases

Breast complaints are common in women and most diseases of the breast (96%) are nonmalignant. Histologic subcategorization of breast masses, based upon cellular proliferation and the presence or absence of hyperplasia, divides these lesions into three subgroups. Nonproliferative lesions include simple and complex cysts. While most cystic lesions do not increase breast cancer risk, complex cysts containing solid and cystic components on ultrasound have increased malignant potential. Proliferative lesions without atypia include fibroadenomas, simple ductal and intraductal hyperplasia, sclerosing adenosis and papillomas. The latter are often associated with unilateral nipple discharge. All of these solid lesions increase breast cancer risk with a relative risk (RR) of 1.6–1.9. Proliferative lesions with atypia (atypical hyperplasia) can be of ductal or lobular origin. They increase the risk of breast cancer 3.7–5.3-fold.

Other common breast disorders include mastitis, cyclical breast pain and nipple discharge. Mastitis affects 3–10% of lactating women and typically presents as unilateral breast pain and high fever. Cyclical breast pain is often related to the hormonal changes of the menstrual cycle. Risk of malignancy after normal exam and imaging of the painful breast is very low. Most women of reproductive age can express discharge from their nipples. However, unilateral discharge, the presence of blood, age greater than 40 and association with a breast mass are concerning and require additional testing.

Breast cancer

Breast cancer is the most common malignancy in women. In addition to occuring almost exclusively in women, it is also a disease of aging. The lifetime risk of developing breast cancer (1 in 8) is largely concentrated in the perimenopausal and postmenopausal years. Risk in the 30-year-old is 1 in 2525, that in a 45-year-old 1 in 93 and that in a 65-year-old 1 in 17. Older women tend to underestimate their risk and many women under 50 years of age grossly overestimate their risk. Consequently, these two groups of women misjudge the benefits of breast cancer screening programs.

Breast cancer can arise anywhere in the mammary gland. Tumors are typically classified by their cells of origin: lobular or ductal. Ductal carcinomas account for 85% of breast cancers and can be either noninvasive (intraductal) or infiltrating. Those ductal carcinomas that are histologically confined by the basement membrane of the duct are called intraductal carcinomas or ductal carcinoma in situ (DCIS). DCIS is considered a precursor lesion to invasive carcinoma. At least 33% of these lesions will progress to invasive cancer within 5 years.

Once the basement membrane of the duct is breached, an infiltrating carcinoma has developed. The most common type of invasive carcinoma is ductal carcinoma, which accounts for 79% of invasive carcinomas. The next most common type is lobular carcinoma. These lesions arise from the terminal ductules of the alveoli and comprise approximately 10% of invasive breast cancers. Less common types of infiltrating carcinomas include medullary carcinomas, mucinous (colloid) carcinomas and Paget disease. Paget disease is a special subtype of infiltrating ductal carcinoma localized to a main lactiferous duct. In Paget disease, eczematous changes develop in the nipple and areola overlying the affected duct. These skin changes are often the first sign of disease although the cancer may have been present for some time.

Breast cancer metastasizes first to the regional axillary lymph nodes. The most frequent distant metastatic sites are bone, liver, lung, pleura and brain. Patients with histologically negative axillary nodes have a much higher likelihood of survival than do patients with positive nodes. The ultimate prognosis for the disease depends on the size of the tumor, the number of involved lymph nodes and whether or not lymphovascular invasion (LVI) is present.

Treatment of invasive breast cancer is typically multimodal, but ultimately depends on the stage of the disease at the time of diagnosis. Surgical options include a modified radical mastectomy or lumpectomy with local irradiation. Ipsilateral axillary lymph node dissection is also typically performed. Women with positive lymph nodes will usually receive additional antineoplastic chemotherapy. Those with negative nodes will receive adjuvant chemotherapy if they have large primary tumors or LVI, because both confer a high risk of tumor recurrence. Tamoxifen is a medication with estrogenic and antiestrogenic properties; it is the most widely used endocrine therapy for breast cancer. Before employing endocrine therapy, it is important to know the estrogen and progesterone receptor status of the tumor because only receptor-positive tumors predictably respond to medications like tamoxifen.

Treatment of DCIS is controversial and includes mastectomy or wide local excision plus irradiation. Recurrence rates following excision plus radiation are approximately 10%; half of these are invasive.