Because breast cancer during pregnancy is relatively rare, only small studies have been done on treating breast cancer during pregnancy. Still, it's very important that pregnant women receive excellent breast cancer care. To ensure this happens, the National Comprehensive Cancer Network (NCCN), a group of 19 leading cancer institutions in the United States, developed guidelines for treating breast cancer during pregnancy. Hundreds of institutions around the world use these guidelines.
The treatment guidelines are different for each stage of pregnancy, so that mother and baby both receive the best possible care.
First trimester: If you've been pregnant for 3 months or less, the guidelines discuss the possibility of ending the pregnancy. The guidelines don't say that you have to end your pregnancy because you've been diagnosed with breast cancer. But it is one of the choices available to you, and it's important to consider all your options when making a decision.
In the first 3 months of pregnancy, if you decide to continue your pregnancy, the next step is mastectomy with axillary lymph node dissection. Mastectomy is recommended over lumpectomy and radiation at this stage of the pregnancy. That's because radiation is not safe during pregnancy. (In women who aren't pregnant, lumpectomy plus radiation may be as effective as mastectomy for those who are candidates.) After surgery, the guidelines suggest beginning chemotherapy in the second trimester. Chemotherapy should not be given during the first trimester. It is important to note that if radiation and hormonal therapy are necessary, they should wait until after the baby is born.
Second trimester: If breast cancer is found during the second trimester of pregnancy, the guidelines recommend either mastectomy or lumpectomy, with axillary lymph node dissection. Chemotherapy could be started before surgery. If you and your doctor opt for lumpectomy, then any necessary radiation therapy and hormonal therapy would be given after your child is born.
Third trimester: The guidelines recommend that if you are diagnosed with breast cancer in your third trimester you have either mastectomy or lumpectomy, with axillary lymph node dissection. Chemotherapy can be safely used if needed. Radiation and hormonal therapy, if necessary, would be given after the baby is born.
The guidelines note that most pregnant women diagnosed with breast cancer have been safely treated with combinations of the chemotherapy medicines Adriamycin (chemical name: doxorubicin), Cytoxan (chemical name: cyclophosphamide), and fluorouracil. The guidelines don't mention the taxanes: Taxol (chemical name: paclitaxel), Abraxane (chemical name: albumin-bound or nab-paclitaxel), or Taxotere (chemical name: docetaxel). A few small studies suggest that the taxanes may be safe to use during the second and third trimesters of pregnancy.
The guidelines also don't mention targeted therapies. Still, the targeted therapies used to treat breast cancer specifically say that they should not be used to treat pregnant women in their prescribing information.