Breast cancer is the most common cancer in pregnant and postpartum women, occurring in about 1 in 3,000 pregnant women. The average patient is between 32 to 38 years of age and, with many women choosing to delay childbearing, it is likely that the incidence of breast cancer during pregnancy will increase.
Breast cancer pathology is similar in age-matched pregnant and nonpregnant women. Hormone receptor assays are usually negative in pregnant breast cancer patients, but this may be the result of receptor binding by high serum estrogen levels associated with the pregnancy. Enzyme immunocytochemical receptor assays, however, are more sensitive than competitive binding assays. A study using binding methods indicated similar receptor positivity between pregnant and nonpregnant women with breast cancer. The study concluded that increased estrogen levels during pregnancy could result in a higher incidence of receptor positivity detected with immunohistochemistry than is detected by radiolabeled ligand binding, which is because of competitive inhibition by high levels of endogenous estrogen.
The natural tenderness and engorgement of the breasts of pregnant and lactating women may hinder detection of discrete masses and, therefore, early diagnoses of breast cancer. Delays in diagnoses are common, with an average reported delay of 5 to 15 months from the onset of symptoms.[2,3,4,5] Because of this delay, cancers are typically detected at a later stage than in a nonpregnant, age-matched population. To detect breast cancer, pregnant and lactating women should practice self-examination and undergo a breast examination as part of the routine prenatal examination by a doctor. If an abnormality is found, diagnostic approaches such as ultrasound and mammography may be used. With proper shielding, mammography poses little risk of radiation exposure to the fetus. Mammograms should only be used, however, to evaluate dominant masses and to locate occult carcinomas in the presence of other suspicious physical findings. Since at least 25% of mammograms in pregnancy may be negative in the presence of cancer, a biopsy is essential for the diagnosis of any palpable mass. Diagnosis may be safely accomplished with a fine-needle aspiration, core biopsy, or excisional biopsy under local anesthesia. To avoid a false-positive diagnosis as a result of misinterpretation of pregnancy-related changes, the pathologist should be advised that the patient is pregnant.