Pregnancy and Cancer
Although cancer treatment can cause infertility in both men and women, if the sperm and ova are viable enough to result in a pregnancy, the baby is unlikely to suffer from congenital defects caused by the sperm and ova's exposure to chemotherapy and radiation therapy. Even though chemotherapy and radiation therapy can cause changes in germ cell DNA, most such changes are not viable, yielding only a slightly increased risk of birth defects.
The primary source of concern is exposure of the fetus to the cancer treatment. Fetuses exposed to chemotherapy during the first trimester are at significantly increased risk of birth defects, because the fetus is exposed to chemotherapy at a critical stage of development. Fetuses should not be exposed to hormone therapy for the duration of the pregnancy and should be shielded from radiation therapy. Women receiving chemotherapy should not breast-feed, as the drugs can pass in breast milk.
Cancer patients are advised to use birth control for the duration of chemotherapy and for several months afterward. (Barrier methods of birth control, such as condoms, are preferred since chemotherapy and hormone therapy can interfere with the effectiveness of hormone-based contraception such as the pill. In addition, some forms of chemotherapy can transfer to your partner through semen and vaginal fluids, although the dose involved is usually very low.) If a woman becomes pregnant while she is receiving chemotherapy, she may need to terminate the pregnancy. Women who may be pregnant should inform their oncologist before starting chemotherapy, hormone therapy or radiation therapy.
Occasionally, a pregnant woman will be diagnosed with cancer, such as breast cancer, leukemia or lymphoma, and will need to undergo chemotherapy, hormone therapy or radiation therapy. This is pretty rare, affecting anywhere from 1 in 2,500 to 1 in 10,000 pregnancies.
Exposure of Fetus to Chemotherapy
Generally, the greatest risk to the fetus occurs during the first trimester and when the chemotherapy involves anti-metabolite drugs. There is a higher risk of birth defects when chemotherapy is given during the first trimester, but not during the second and third trimesters.
There is also a risk to the fetus of infection and hemorrhage, caused by myelosuppression. Chemotherapy can cause lower red blood cell counts, white blood cell counts and platelet counts in the fetus just as it does in the patient.
Very little is known about the long-term effects of chemotherapy on the fetus. A few small studies have suggested that there is no increased risk of birth defects, mental retardation or malignancies if chemotherapy is given after the first trimester.
Meistrich and Byrne 2002 report that offspring of cancer patients receiving potentially mutagenic chemotherapy did not exhibit a significantly higher incidence of genetic diseases. However, the male-to-female ratio among the offspring was significantly lower than in the general population. Note that this study was unable to rule out the possibility of an increase in risk of genetic diseases of 76% or less.
There is a tendency toward premature delivery among pregnant women receiving chemotherapy, but it does not appear to otherwise affect the outcome of the pregnancy.
Thus a good rule of thumb is to wait until the second trimester to begin chemotherapy. (See Ring 2005.) If the cancer is diagnosed within a few weeks of the due date, it may be possible to delay the start of therapy until after delivery, eliminating any possibility of risk to the fetus. However, pregnancy often delays the diagnosis of cancer, causing the cancer to be discovered at a more advanced stage. In such situations the oncologist may not want to wait to start chemotherapy. The oncologist may also want to start chemotherapy immediately for certain very aggressive forms of cancer.
During the second and third trimester the oncologist should carefully consider which chemotherapy agents to give. Certain large molecule drugs, such as Adriamycin and Cytoxan, do not pass through the placenta and so are safe for the fetus. Other drugs are known to be harmful. For example, Procarbazine has been linked with birth defects when given during the first trimester. Hormonal drugs like Tamoxifen should also be avoided for the duration of the pregnancy.
Nursing and Chemotherapy
Women who are receiving chemotherapy or hormone therapy should not breast feed, as the drugs can be passed to the infant in breast milk. The data sheets for most cytotoxic drugs do not address whether the drug is passed in breast milk, but most drugs taken by the mother are detectable in breast milk.
Exposure of Fetus to Radiation Therapy and X-rays
Radiation therapy can be given if it is possible to shield the fetus sufficiently from direct and scatter radiation. MRI and ultrasound should be preferred for imaging studies, to minimize exposure to ionizing radiation from X-rays and CT scans, although a chest X-ray can be given with adequate shielding.
Surgery During Pregnancy
Surgery to remove tumors can be performed during pregnancy. The main risk is from anesthesia. If proper precautions are taken, this risk can be minimized. Abdominal surgery, however, can be more complicated.
Cancer Survivors and Pregnancy
Most female cancer survivors should wait two years after the end of treatment before trying to have a baby. This is not just to allow for recovery of fertility, but because the greatest chance of a relapse is within the first two years after treatment. Waiting two years minimizes the likelihoohd that a female cancer survivor will need to terminate the pregnancy because of a relapse, or delay a resumption of treatment because of the pregnancy.
Pregnancy does not increase the risk of a relapse among women who were previously treated for stage I or stage II breast cancer.
Male cancer survivors do not have to wait two years to try impregnating their partners, but should be patient because of the fertility issues. As discussed in the cancer and infertility page, certain forms of cancer treatment can cause temporary sterility that lasts for six months to two years.
Cancer survivors often wonder whether they should have children, since there is always a chance of a relapse. They worry about depriving their child of a parent or their partner of a source of financial support. These concerns should be discussed with your doctor, who can provide you information about your chances for a relapse. A good rule of thumb is to wait until the risk of a relapse had dropped below 1% per year. For many cancer survivors the highest risk of a relapse is the first two years after the end of treatment.
Cancer survivors may also be concerned about the possibility that their cancer is hereditary and can be passed on to their children. However, for most hereditary forms of cancer there is only a 50% risk of passing on a cancer susceptibility genere, and even if the child has the gene, that does not guarantee that they will get cancer. Medical advances are also reducing the risk of passing on a genetic propensity for cancer. For example, preimplantation genetic diagnosis (PGD) can be used with IVF and ICSI to test an embryo for a hereditary condition before implanting the embryo in the uterus.
Other Resources
A good resource on the topic of pregnancy and cancer is the Pregant With Cancer Network.
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