Pregnancy-associated breast cancer (PABC) is defined as breast cancer diagnosed during pregnancy and/or including the first year following childbirth (or postpartum). PABC has an incidence of about 1 in 3,000 pregnancies and is the second most common malignancy seen in pregnant women after cancer of the cervix. As more women delay childbearing for personal or professional reasons, the diagnosis of breast cancer during or before the completion of childbearing may occur more often. The median age of diagnosis is 33 years.

A delay in diagnosis can be due to patient denial or physician reluctance to intervene during pregnancy. Additionally hormonal influence of the pregnancy on breast tissue affects the ability to detect a mass during pregnancy. Physical examination of the breast becomes increasingly more difficult as the pregnancy progresses or during the postpartum period if lactation is established. Prompt evaluation of a breast mass with or without biopsy is thus warranted. Ultrasound is the preferred method of imaging for evaluation of a breast mass in pregnancy and is often the first step. Mammography has a low risk of radiation, especially with abdominal shielding, but often is not informative because young women of childbearing age frequently have dense breasts.

Eighty percent of cancers are infiltrating ductal carcinomas, high grade with lymphovascular invasion, estrogen receptor and progesterone receptor negative (70%), and/or have positive lymph nodes (67%). When age- and stage-matched, PABC does not have a worse prognosis than non-PABC; however, it is more often diagnosed at later stages.

Mastectomy is usually recommended in the first 2 trimesters. In the third trimester, the patient has the option of a lumpectomy followed by radiation therapy. The radiation therapy is delayed until after the postpartum period. Alternatively, neoadjuvant chemotherapy (chemotherapy given before surgery) or lumpectomy followed by adjuvant chemotherapy and then postpartum radiation can be considered dependent on the type and stage of the breast cancer or patient choice.

Chemotherapeutic treatment regimens for PABC should be the same as those prescribed for nonpregnant patients. Tamoxifen has a 20% risk of birth defects and is therefore contraindicated during pregnancy. Chemotherapy administered during the first trimester poses the highest risk of fetal birth defects (teratogenesis), with an increased risk associated with multi-agent therapy. It is also recommended that chemotherapy be discontinued 3 weeks prior to delivery due to the risk of bone marrow (hematopoietic) suppression in mother and newborn and to prevent drug accumulation in the newborn.

In conclusion, prompt evaluation of a breast mass in pregnancy is warranted to avoid a potential delay in diagnosis. The treatment of breast cancer in pregnancy is the same as that outside of pregnancy, with some modifications for fetal indications.