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Carcinoma of the breast (see also Chapter 17) is one of the most commonly diagnosed cancers in pregnancy. Although the effects of pregnancy on breast cancer progression are unclear, it has been consistently reported that breast cancers diagnosed during pregnancy are more likely to have higher grade disease with associated nodal involvement when compared with those diagnosed in nonpregnant women.

Eighty percent of pregnancy-associated breast cancer is infiltrating ductal carcinoma, 49–84% are estrogen receptor/progesterone receptor–negative, 28–58% are HER2/neu overexpressed, and about 67% present with positive lymph nodes.

Delay in diagnosis can occur because of a patient's confusion between cancer-related changes and pregnancy-related changes of the breast. Prompt evaluation of any breast mass is warranted. Ultrasonography is the preferred imaging method for breast mass evaluation during pregnancy, allowing for ultrasound-guided biopsy, if necessary. Mammography, if needed for further evaluation, has a low risk of radiation, especially with abdominal shielding.

Treatment of breast cancer in pregnancy is similar to that in nonpregnancy, with modifications for fetal indications. There is no evidence that therapeutic abortion improves maternal survival, and such management is only indicated when progressive development of malignancy is expected or fetal harm from continued intensive adjuvant therapy is likely. Mastectomy is generally recommended in the first and second trimesters. Breast and axillary surgery can be performed during any trimester of pregnancy with minimal risk to the fetus, especially after 12 weeks when the risk of spontaneous miscarriage is minimal. Due to a decreased risk of miscarriage with surgery after the first trimester, surgery should be deferred to the second or third trimester if possible. Lumpectomy can be performed during the third trimester with delay of radiation therapy to the postpartum period. Neoadjuvant chemotherapy or lumpectomy followed by adjuvant chemotherapy can be administered during pregnancy for oncologic reasons, or patient choice, if remote from delivery.

The decision to breastfeed should be made on a case-by-case basis and depends largely on what the treatment plan is during the postpartum period.

Cordeiro  CN  et al. Breast cancer in pregnancy: avoiding fetal harm when maternal treatment is necessary. Breast J. 2017;23:200.
[PubMed: 28191695]  
Macdonald  HR. Pregnancy associated breast cancer. Breast J. 2020;26:81.
[PubMed: 31943583]  

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