Breast cancer

Breast cancer is the most common cancer affecting women and is the number two killer (after lung cancer) of women ages 35 to 54. It occurs in men, though only rarely. (See Breast cancer in men.) The overall breast cancer death rate for American women has fallen. Lymph node involvement is the most valuable prognostic predictor. With adjuvant therapy, 70% to 75% of women with negative nodes will survive 10 years or more, compared with 20% to 25% of women with positive nodes.

Although breast cancer may develop anytime after puberty, it’s most common after age 50.

Causes

The cause of breast cancer is unknown, but its high incidence in women implicates estrogen. Certain predisposing factors are clear; women at high risk include those who:

have a family history of breast cancer
have long menses; began menses early or menopause late
have never been pregnant
were first pregnant after age 31
have had unilateral breast cancer
have had endometrial or ovarian cancer
have been exposed to low-level ionizing radiation.

Many other predisposing factors have been investigated, including estrogen therapy, antihypertensives, high-fat diet, obesity, and fibrocystic disease of the breasts.

Women at lower risk include those who:

were pregnant before age 20
have had multiple pregnancies
are Indian or Asian.

Pathophysiology

Breast cancer is more common in the left breast than in the right and more common in the upper outer quadrant. Growth rates vary. Theoretically, slow-growing breast cancer may take up to 8 years to become palpable at 1 cm in size. It spreads by way of the lymphatic system and the bloodstream, through the right side of the heart to the lungs and, eventually, to the other breast, the chest wall, liver, bone, and brain.

Many refer to the estimated growth rate of breast cancer as doubling time, or the time it takes the malignant cells to double in number. Survival time for breast cancer is based on tumor size and spread; the number of involved nodes is the single most important factor in predicting survival time.

Classified by histologic appearance and location of the lesion, breast cancer may be:

adenocarcinoma—arising from the epithelium
intraductal—developing within the ducts (includes Paget’s disease)
infiltrating—occurring in parenchymatous tissue of the breast
inflammatory (rare)—reflecting rapid tumor growth, in which the overlying skin becomes edematous, inflamed, and indurated
lobular carcinoma in situ—reflecting tumor growth involving lobes of glandular tissue
medullary or circumscribed—a large tumor with a rapid growth rate.