Breast cancer is a problem of major importance to the practicing physician for the following reasons:

1. It is the most common cancer among women. Estimates indicate that I of every 20 women in the United States will develop breast cancer during her lifetime.

2. The differential diagnosis of breast lesions is a common office problem, with cancer an ever-present possibility.

3. The breast is readily accessible to examination by the physician and the patient. Furthermore, the prognosis has been related clearly to the size of the tumor when first diagnosed and treated (i.e., the smaller the lesion, the better the chances for long-term survival).

Epidemiology. Incidence

Mortality

Rates And Ratios

Age

Trend Last Ten Years

Marital Status, Parity, And Nursing Factors

The incidence of breast cancer in women decreases in the following order:

1. Virginal women (highest)

2. Nulliparous women

3. Parous women who have nursed their infants

4. Multiparous women who have not nursed their infants (lowest)

Other factors being equal, the risk of developing breast cancer is lowest in women who bear and nurse several children.

Family History

There is a demonstrable familial factor for cancer of the breast. Numerous epidemiologic studies indicate that daughters and sisters of breast cancer patients have two to three times the normal risk of developing this disease. However, there is a variation between families in the relative importance of the familial factor which requires further study. Until this is further clarified, it is reasonable to assign those individuals with a strong family history of breast cancer to a potentially high-risk group.

Racial And Ethnic Differences

Japanese women have the lowest reported rates of breast cancer in the world and Danish and Scottish women the highest. Epidemiologic studies indicate that these contrasts are not adequately explained by differences in pregnancy and nursing factors and suggest that the intrinsic endocrine factors have etiologic significance.

In the United States there is a somewhat lower rate of breast cancer in Negro women. This may be fully accounted for by the factors of multiparity and nursing.

The geographic distribution of breast cancer in women is given in Table 6.

Left Breast Vs. Right Breast

Cancer is more common in the left breast than in the right breast in a ratio approximating 11:10.

Benign Breast Disease

A relationship between chronic fibrocystic mastitis (mastopathy) and subsequent development of cancer has been proposed by some investigators and denied by others. The question is complicated by the frequency and variability of benign mastopathy and the difficulties of clinical and pathologic diagnosis. Whatever the ultimate resolution of this controversy, in practice particular attention should be paid to the patient with mastopathy since the benign condition may camouflage a malignant process.

Table 6. Geographic Distribution Of Breast Cancer In Women (Annual Mortality Rates Per 100,000,1956-1957)

Age-adjusted on combined population of forty-six countries in 1950. *From Segi, M.: Cancer Mortality for Selected Sites in Twenty-Four Countries (1950-1957), Sendai, Japan, 1960, Tohoku University School of Medicine.

Other Disease

An increased frequency of endocrine abnormalities of the type associated with hyperestrinism and with diabetes has been noted in breast cancer patients. There is suggestive evidence of a decreased incidence of breast cancer in women castrated before the age of 38 years-hardly a practical approach.

Other Factors

There is no established evidence that human breast cancer is related to the following:

1. Trauma

2. Hormone therapy

3. Breast size or configuration

4. A milk factor transmitted from the mother by nursing

Etiology

The etiology of breast cancer is unknown. The epidemiologic evidence noted previously suggests a few factors which may predispose an individual to the disease. The question of benign breast disease as a precursor of cancer has been referred to previously.

Certainly it is likely that hormonal influences are of major importance in the causation of breast cancer. Present knowledge does not permit more than this rather vague generalization, however.