358Cancer in Pregnancy

Cancer occurs in one woman per every 1,000 live births, with approximately 4,000 cases of concurrent pregnancy and maternal malignancy each year. The most common cancer in pregnancy is breast cancer. The most common cancer of the female reproductive system in pregnancy is cervical cancer.

•   If cancer is diagnosed prior to 24 weeks gestation, the patient can decide to terminate the pregnancy.

•   If a malignancy is diagnosed after fetal viability, treatment can be delayed until the late second trimester, third trimester, or after delivery, depending on the specific clinical situation.

RADIATION THERAPY IN PREGNANCY

Radiation therapy (XRT) has different effects on a fetus depending on the stage of fetal development at the time of radiation exposure.

•   At preimplantation, the effects are “all or nothing” meaning that XRT will either kill the embryo or not affect it at all, although there are recent reports of increased rates of fetal malformations with XRT prior to implantation.

•   Organogenesis occurs 8 weeks after fertilization. The main fetal effect of XRT during organogenesis is intrauterine growth restriction but a wide array of congenital structural deformities can occur. With doses of greater than 1 Gy, morphologic anomalies, and mental retardation, may develop.

•   The main effect of XRT in the fetal stage is resultant cognitive impairment. The central nervous system (CNS) is the most sensitive until about 25 weeks. Intrauterine growth restriction can also occur with doses greater than 0.5 Gy.

•   The recommended maximum dose of XRT during pregnancy is 0.5 Gy (Table 6.2).

•   There are three principal sources of XRT exposure to the fetus during maternal XRT: photon leakage through the treatment head of the machine, scatter XRT emanating from the imaging equipment, and internal scatter within the mother from the treatment beams. Fetal XRT exposure can be reduced by external shielding, but internal scatter cannot be modified.

CHEMOTHERAPY IN PREGNANCY

•   The background rate of fetal anomalies for all pregnancies is 2% to 3%. The risk of anomalies with chemotherapy in the first trimester is 6% using a single-agent drug regimen and 17% with combination therapy. If folate antagonists are excluded, the risk is reduced to 6%.

•   Chemotherapeutic agents commonly used during pregnancy are vinca alkaloids, doxorubicin, and cisplatin. Alkylators such as cisplatin and doxorubicin can carry a 14% risk of fetal anomalies in the first trimester and 4% in the second trimester. Vinca alkaloids are particularly useful during the first trimester and do not cross the placenta. Doxorubicin can be used in the first trimester of pregnancy. The multidrug resistance (MDR1) P-glycoprotein is found in higher amounts of the endometrium and placenta. MDR1 may provide protection for the fetus. Cisplatin can cause a 50% risk of intrauterine growth restriction, bilateral neonatal hearing loss, or leukopenia. Antimetabolites can cause cranial nasal dystocia, auditory malformations, micrognathia, and limb deformities.

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