A cancer diagnosis during pregnancy is very rare. Little research has been done about cancer during pregnancy. It is known that in some cases a pregnant woman with cancer is able to give birth to a healthy baby and also that certain cancer treatments are safe during pregnancy or during certain times of pregnancy.
Incidence
Approximately one out of every 1,000 women will be diagnosed with cancer while she is pregnant. Pregnancy itself does not cause cancer and pregnant women do not have an increased risk of developing cancer compared to women who are not pregnant. The cancers that tend to occur during pregnancy are those that are more common in younger people or have the highest incidence during the reproductive years. Some of the most common cancers diagnosed during pregnancy include:
- breast cancer – the most common
- cervical cancer
- Hodgkin's disease and non-Hodgkin's lymphoma
- ovarian cancer
- malignant melanoma
- leukemia
- thyroid cancer
Other types of cancers such as brain tumours, bone cancer, lung cancer and liver cancer (hepatocellular carcinoma) can occur when a woman is pregnant, but are very rare.
It is expected that the rate of cancer during pregnancy will increase as more women are waiting until they are older to have children.
Diagnosing cancer during pregnancy
Many symptoms such as nausea, vomiting, abdominal bloating, fatigue or headaches are common during pregnancy and are often not considered suspicious. Occasionally some of these same symptoms can be related to a particular type of cancer and being pregnant may delay a cancer diagnosis. For example, enlarging and tender breasts during pregnancy can make it hard to detect small breast tumours and mammograms are not routinely done during pregnancy, so a breast cancer may go undetected for awhile.
Pregnant women and their doctors may be concerned about using diagnostic tests such as x-rays, computed tomography (CT) scans or nuclear medicine tests that use radioisotopes, if cancer is suspected. Research has shown that the level of radiation in diagnostic x-rays is quite low and may not be harmful to the fetus. This depends on the age of the fetus, the number of x-rays used, the amount of radiation exposure and whether or not the fetus is directly exposed to radiation. Whenever possible, a lead shield is used to cover the mother's abdomen and offers extra protection.
Diagnostic tests, such as magnetic resonance imaging (MRI) and ultrasound, are usually considered safe during pregnancy because they do not use radiation. Physical examination and many biopsies are also safe and important in arriving at a cancer diagnosis.
Sometimes pregnancy can uncover cancer that has gone undetected. For example, a Pap test is often done as part of a woman's routine care during pregnancy and can detect cervical cancer. Routine ultrasounds done during pregnancy may detect ovarian cancer.
Cancer treatment during pregnancy
Treating cancer during pregnancy is very complex. The best treatment for the mother and the possible risks or harm to the fetus are considered when looking at treatment options. The type of treatment and when it may be given depends on many factors:
- the location of the cancer
- the type of cancer
- the size of the tumour or stage of the cancer
- the stage of the pregnancy (how old the fetus is)
- the wishes of the mother and her partner
Treatment is tailored to each woman. Cancer treatments used during pregnancy may include surgery, chemotherapy and sometimes radiation therapy, but these are only used after careful consideration and planning to ensure the mother and baby's safety.
- Some cancer treatments can harm a fetus, especially during the first three months of pregnancy, called the first trimester. Sometimes cancer treatment may be delayed until later in the pregnancy, during the second or third trimester.
- When cancer is diagnosed later in a pregnancy, sometimes it may be possible to wait to start treatment until after the baby is born. The doctor may also consider bringing on labour early.
- For some very early stage cancers, such as very early stage cervical cancer, it may be safe to continue the pregnancy to term and delay treatment until after the baby is born.
- In some situations the woman, her partner and the doctor need to discuss whether or not to continue with the pregnancy. Not delaying treatment may be the safest option for some women with more advanced or aggressive cancers found early in a pregnancy.
Surgery
Most biopsies can safely be done during pregnancy using a local anesthetic. Generally, surgery poses the least risk to the fetus and may be considered the safest cancer treatment option for some cancers, especially after the first trimester. Improvements in surgery and anesthetics, and careful monitoring of the mother and baby, make it possible to keep risks to a minimum. In some cases, more extensive surgery may be done to avoid having to use chemotherapy or radiation therapy.
Chemotherapy
Chemotherapy is the use of anti-cancer drugs to treat cancer. It is a systemic therapy that travels throughout the body and destroys cancer cells. Chemotherapy drugs are toxic and have the potential to harm a fetus, especially if they are given during the first trimester of pregnancy, when the fetus’ organs are still developing.
- Chemotherapy during the first trimester can cause birth defects, low birth weights or may cause a woman to miscarry. The risk of birth defects when chemotherapy is given during the first trimester is estimated to be about 10%.
- Some effects of chemotherapy on a fetus are also not known, especially for newer drugs like biological therapies or targeted therapies.
- Often these drugs are not recommended to be used during pregnancy or breast-feeding.
Some chemotherapy drugs may be given during the second and third trimesters without causing harm to the fetus. Protection is provided by the placenta. The placenta develops during pregnancy and connects the blood supplies of the mother and baby. It provides nutrients and removes waste products. It also acts as a barrier between the mother and the fetus that many chemotherapy drugs cannot pass through. However, chemotherapy given during the second and third trimesters is associated with early labour and low birth weight.
Chemotherapy can also cause health problems in the mother such as infection, anemia or nausea and vomiting that may indirectly harm a fetus.
Radiation therapy
Radiation therapy uses high-energy rays or particles to destroy cancer cells and shrink tumours. Radiation can harm a fetus, especially during the first trimester when the baby's organs and nervous system are developing, so radiation treatment is usually not recommended during this time. Whether or not radiation therapy can be used in the second or third trimesters depends on the dose of radiation and the area of the body being treated.
When radiation therapy is possible, careful planning is used when treating pregnant women with cancers that are far away from the pelvis (such as breast cancer or head and neck cancers). Lead shields or blocks are used to reduce the amount of radiation exposure to the fetus as much as possible. Cancers in the pelvis in a pregnant woman cannot be treated effectively with radiation therapy without causing severe problems for the fetus.
Prognosis
In many cases, the prognosis of a pregnant woman with cancer is the same as that of any other woman of the same age with the same type and stage of cancer. If a cancer diagnosis is delayed because of pregnancy, these women may have a poorer overall prognosis than women who are not pregnant and are diagnosed earlier.
Pregnancy may affect the behaviour of some cancers. For example, there is some evidence to suggest that hormone changes that occur during pregnancy may stimulate malignant melanoma to grow.
Effect on the fetus
Cancer rarely affects the fetus directly. Only a few cancers can spread from the mother to the fetus. These include malignant melanoma, non-Hodgkin's lymphoma and leukemia. The undesirable effects of cancer during pregnancy on the developing fetus are largely unknown.
Breast-feeding
Cancer cells cannot pass to the infant through breast milk, but women being treated for cancer are often advised not to breastfeed. Women receiving chemotherapy should not breastfeed, because chemotherapy drugs can build up in breast milk, are toxic and can harm the infant.
Radiopharmaceuticals are radioactive substances that may be taken by mouth (such as radioactive iodine) or are given by injection for certain nuclear medicine tests and procedures. These also cross into breast milk and can harm the infant.
The healthcare team will make recommendations about how long a woman should not breast-feed after receiving any radiopharmaceuticals. They may also suggest using a breast pump and getting rid of breast milk for a time after procedures that use radiopharmaceuticals. Any recommendations will be based on the particular radioactive substance used.
Sometimes it is okay for a woman to pump and freeze her breast milk before a nuclear medicine procedure and this milk may be given to the infant while breast-feeding is not advised.
Always look to the healthcare team for instructions on what to do about breast-feeding and whether it is safe or not.