Breast cancer is the most common type of cancer among women. It often begins in lobules or ducts of the breast tissue; it can spread when the cancer cells get into the blood or lymph system. Every year in the United States, one in 3,000 women will be diagnosed with breast cancer during pregnancy. There is no evidence that breast cancer itself can harm a woman’s baby, so during this challenging time, doctors try to protect the growing fetus while curing or controlling the cancer whenever possible.

If a woman is pregnant and diagnosed with breast cancer, or is diagnosed with breast cancer and becomes pregnant, there can be many factors to consider when deciding on a treatment strategy. These include the size of the tumor, the location of the tumor, if the cancer has spread, how far along the pregnancy is, the patient’s overall health, and the woman’s personal preferences.

In general, surgery is a safe treatment for pregnant women. Decisions about mastectomy or lumpectomy not only depend on tumor features (e.g. size) but also on the timing of pregnancy, because a lumpectomy usually requires radiation therapy afterward, which can negatively affect the baby.

If a woman is late in the pregnancy, radiation can be deferred until after delivery, and if a patient is early in pregnancy and needs chemotherapy, then waiting on radiation is also often reasonable. However, waiting too long may impact the efficacy of the radiation and therefore sometimes a mastectomy will be preferred in that setting to avoid unnecessary delays.

Another standard treatment after breast cancer, chemotherapy, is typically safe in the second and third trimester of pregnancy but not the first. The first trimester is when most of the baby’s organs develop and the risk of miscarriage is highest. Chemotherapy can also lower the mother’s blood cell counts, so it is not recommended close to the peripartum period (soon before or after delivery).

Other adjuvant therapies, such as radiation therapy, hormone therapy, and targeted therapy, must be held off until after delivery.

Some women may be able to breastfeed their child after a lumpectomy and radiation therapy, even though these procedures can reduce milk production and alter breast structure. Women who undergo a single mastectomy can breastfeed with the remaining breast. Double mastectomy patients are unable to breastfeed. Breastfeeding is safe for the mother and the baby if she is not undergoing chemotherapy or taking hormone and targeted therapy drugs. These substances can enter the breast milk and be passed on to the baby.

Breastfeeding after breast cancer treatment does not appear to increase risk of recurrence. In fact, some research suggests that having a history of breastfeeding might lower the risk of the cancer coming back.

A study showed that women who had been treated early for breast cancer and went on to have children did not have a higher risk of their breast cancer recurring than survivors who did not become pregnant.
A study is testing whether it’s safe for breast cancer survivors who want to get pregnant to temporarily stop taking hormone-blocking drugs, such as tamoxifen, for hormone-positive breast cancer. These drugs are usually recommended for at least five years after initial treatment to help prevent recurrence.

Although many women are able to get pregnant after breast cancer treatment, certain treatments, such as chemotherapy, might damage the ovaries and cause immediate or delayed reproductive complications, such as infertility. If a patient is diagnosed with breast cancer and foresees getting pregnant in the future, she should talk to her doctor before starting breast cancer treatment and consider pursuing fertility preservation.