Cancer drugs. (Drugs, Pregnancy, and Lactation).

Cancer in pregnancy is an extremely stressful, complex situation. First, the issues of whether the cancer affects the pregnancy and whether the pregnancy affects the cancer should be considered. For example, breast cancer, which is probably the most common cancer diagnosed in pregnancy may be sensitive to hormones, raising the issue of whether pregnancy itself may accelerate cancer growth.

Data indicate that cancer prognosis in general is not affected by pregnancy. Studies suggest that at each stage of breast cancer, prognosis is not affected by pregnancy, and remission rates and survival times for pregnant women with leukemia are similar to rates among nonpregnant women.

In contrast, pregnant breast cancer patients do have a much higher risk of metastatic disease upon diagnosis. Whether this is due to hormones is not clear; it probably is at least partially due to breast engorgement, which makes it more difficult to detect a cancer.

Since the mechanism of all cancer chemotherapy drugs involves arresting cell division, these agents are potent teratogens, so use during the first trimester should be avoided.

In our experience, many women choose to terminate the pregnancy when cancer is diagnosed in the first trimester. If a woman chooses to keep the pregnancy, one approach is to wait until 12-14 weeks' gestation before starting treatment.

Some women aren't aware that they have conceived while undergoing chemotherapy and continue treatment through the first trimester. The estimated risk of malformations associated with first-trimester exposure is 10% when one agent is used and 25% with a combination of agents.

Although there is no evidence that exposure to cancer chemotherapy drugs in the second and third trimesters increases the risk of malformations, other concerns remain. There have been reports of an increased risk of stillbirth, low birth weight, and intrauterine growth retardation in babies whose mothers received chemotherapy in the second and third trimesters.