19 Cancer in pregnancy
Cancer during pregnancy poses a very challenging situation. Cancer complicates 0.02–0.1% of pregnancies. The oncologist faces the difficult situation of optimizing the care of the mother without causing harm to the foetus. The common tumours diagnosed during pregnancy are malignant melanoma, breast cancer and cervical cancer.
Diagnostic work-up
All patients require a complete physical examination. Although histological diagnosis with fine needle aspiration cytology and core biopsies are safe, general anaesthesia during the first trimester carries a 1–2% risk of spontaneous abortion. Endoscopic biopsies as well as lumbar puncture and bone marrow examinations are safe. Radiological investigations should be restricted to minimize the foetal exposure to ionizing radiation. A foetal exposure dose of 1 mGy is considered safe. Box 19.1 shows various imaging procedures and uterine/foetal exposure dose. A dose of less than 100 mGy (10 cGy) is associated with less than 1% risk of foetal malformation and carcinogenesis and hence, in the event of inadvertent exposure of pregnant women to radiation, termination of pregnancy is not recommended if the foetal dose does not exceed this limit.
Box 19.1
Uterine/foetal radiation dose during various radiological investigations
| Investigation | Uterine/foetal dose |
|---|---|
| Chest X-ray | 0.000005 Gy |
| Abdominal X-ray | 0.022 Gy |
| Mammogram | 0.04 Gy |
| Chest CT scan | 0.002 Gy |
| Abdominal CT scan | 0.02 Gy |
| Pelvic CT | 0.07 Gy |
| Barium enema | 0.036 Gy |
| IVU | 0.045 Gy |
| Bone scan | 0.018–0.045 Gy |
1 Gy = 100 cGy = 1000 mGy
Surgery
Surgery can be performed without major risk to the patient during the first two trimesters, but with a 1–2% risk of foetal loss, small risk of low birth weight (RR 1.5–2.0) and premature delivery. Foetal harm during surgery is due to various factors including placental transfer of drugs, intraoperative complications such as hypoxia, hypotension, and long-term supine positioning of mother during surgery causing placental underperfusion.
Radiotherapy
The developing embryo or foetus is extremely sensitive to ionizing radiation, which can cause foetal loss, malformations, growth retardation and defects in intelligence. Radiotherapy is therefore contraindicated for abdominal and pelvic malignancies during pregnancy. Several studies support the use of radiotherapy for head and neck cancer, breast cancer and brain tumours. Radical radiotherapy to the head and neck and brain can be achieved with a foetal dose of less than 100 mGy (Box 19.2). During radiotherapy to the breast and chest wall, the dose to the foetus increases with gestational age. The foetal dose depends on the radiation field, dose, the distance between the edge of radiation field and foetus, and the machine and its shielding measures.
