Pregnancy and Breast Cancer

Very few pregnant women are diagnosed with breast cancer. But because more women are choosing to have children later in life, and because the risk of breast cancer increases as women age, there may be more cases in the future. For instance, only 1 in 50 breast cancers are found in woman under 35, but about 1 in 9 breast cancers are found in women aged 35 to 44. Women age 45 and older have an even higher risk.

Estimates are that about 1 out of 3,000 pregnant women is diagnosed with breast cancer.

Breast cancer risk

What is cancer?

Normal body cells grow, divide, and die in an orderly fashion. During the early years of a person's life, normal cells divide more quickly until the person becomes an adult. After that, cells in most parts of the body divide only to replace worn-out or dying cells and to repair injuries.

Because cancer cells keep on growing and dividing, they are different from normal cells. Instead of dying, they outlive normal cells and keep making new, abnormal cells. Hormones like estrogen help normal breast cells grow and divide, but they can also promote the growth of breast cancer cells.

How your menstrual cycles affect breast cancer risk

Women who are exposed to higher levels of estrogen over longer periods of time seem to have a slightly higher risk for breast cancer. This includes women who had more menstrual periods, such as those who started menstruating before age 12 or who went through menopause after age 55.

How pregnancy affects breast cancer risk later in life

Pregnancy causes many hormone changes in the body. For one thing, pregnancy stops the monthly menstrual cycles and shifts the hormone balance toward progesterone rather than estrogen. This is why women who go through a pregnancy while they are young may have a slightly lower risk of breast cancer later on. Women who have had no children or who had their first pregnancy after age 30 have a slightly higher breast cancer risk later in life.

How breast-feeding affects breast cancer risk

Some studies have suggested that breast-feeding may slightly lower breast cancer risk. This is more likely if breast-feeding goes on for 1½ to 2 years or if many children are breast-fed. The reason for this may be that both pregnancy and breast-feeding reduce a woman's total number of lifetime menstrual cycles. But new information suggests that breast-feeding may also affect the level of another hormone, called prolactin. A 2008 study showed that women who breast-fed a baby for a year or more had lower prolactin levels for the rest their lives, whether or not they ever breast-fed again. This may also help lower breast cancer risk later on. More research is needed to look into the effects of breast-feeding.

Finding breast cancer during pregnancy

When a pregnant woman develops breast cancer, it is often diagnosed at a later stage than it is in women who are not pregnant. This is partly because during pregnancy hormone changes cause a woman's breasts to get larger, tender, and lumpy. This can make it harder for you or your doctor to find a lump in your breasts. Mammograms are also harder for doctors to read during pregnancy because the breast tissue becomes denser. The early changes caused by cancer could be mistaken for or hidden by the normal changes that happen with pregnancy.

Mammograms can detect most of the cancers that start during pregnancy. But screening may be postponed because some patients (and even doctors) worry about the safety of doing a mammogram during pregnancy.

It is fairly safe to have a mammogram during pregnancy. The amount of radiation needed for a mammogram is small. And the radiation is focused on the breast so that most of it does not reach other parts of the body. For extra protection, a lead shield is placed over the lower part of the belly to stop radiation from reaching the womb. Still, scientists can't be certain about the effects of even a small dose of radiation on an unborn baby. If your doctor does not believe you need to have your mammogram right away, it may be best to wait. Other imaging tests that do not use radiation, such as breast ultrasound, may be used instead. These are thought to be safe alternatives to mammograms during pregnancy.

Even during pregnancy, early detection is an important part of breast health. Talk to your doctor or nurse about breast exams and the best time for your next mammogram, especially if you are age 40 or older, or if you or your doctor notices a change in how your breasts look or feel. As always, if you find any lump or change in your breasts, tell your doctor or nurse right away.

Breast cancer diagnosis and staging during pregnancy

Biopsy

A new lump or abnormal imaging test result may cause concern, but a biopsy is needed to find out if it is breast cancer. During a biopsy a piece of tissue is taken from the area the doctors are concerned about. This is usually done either using a long, hollow needle or through a small surgical incision (cut). A breast biopsy during pregnancy can usually be done as an outpatient procedure. The doctor uses medicine to numb just the area of the breast involved in the biopsy. This causes little risk to the fetus. But the biopsy can be done under general anesthesia (where drugs are used to put the patient into a deep sleep) if needed, with only a small risk to the fetus.

Tests to learn the cancer stage

If breast cancer has been found, other tests may be needed to find out if cancer cells have spread within the breast or to other parts of the body. This process is called staging. Staging tests are very important for pregnant women with breast cancer because their cancers tend to be found at a more advanced stage. Which staging tests may be needed depends on your case.

Keep in mind that the fetus is not exposed to radiation with tests like ultrasound and magnetic resonance imaging (MRI) scans. Overall, these tests are thought to be safe and can be used if they are important to your care. But the contrast material (dye) sometimes used in MRI crosses the placenta, the organ that connects the mother to the fetus. It has been linked with fetal abnormalities in lab animals. For this reason, an MRI that uses contrast dye is not recommended during pregnancy. But an MRI without contrast can be used if needed.

Chest x-rays, sometimes needed to help make treatment decisions, use a small amount of radiation. They are thought to be safe for pregnant women when the belly is shielded.

Other tests, such as bone scans or computed tomography (CT) scans of the chest, abdomen (belly), or pelvis, are more likely to expose the fetus to radiation. These tests are not often needed, especially if the cancer is thought to be just in the breast. In rare cases when these scans are needed, doctors can adjust the way the test is done to limit the amount of radiation the fetus is exposed to.

In very few cases, the cancer has reached the placenta (the organ that connects the mother to the fetus). This could affect the amount of nutrition the fetus gets from the mother, but there are no reported cases of breast cancer being transferred from the mother to the fetus.

Breast cancer treatment during pregnancy

If breast cancer is found during pregnancy, the type and timing of treatment depends on many things, such as:

• The size of the tumor
• Where the tumor is
• How far along the pregnancy is
• What the woman prefers

Treating a pregnant woman with breast cancer has the same goals as treating a non-pregnant woman: control the cancer in the place where it started and keep it from spreading. But protecting a growing embryo or fetus may make reaching these goals more complex.

If a pregnant woman needs chemotherapy, hormone therapy, or radiation therapy to treat breast cancer, she may be asked to think about ending the pregnancy. This is because these treatments may harm the fetus. It is easier to treat a woman who is not pregnant because there is no fear of harming the fetus. But no studies have proven that ending a pregnancy in order to have cancer treatment improves the woman's prognosis (outlook for survival). These issues are discussed in more detail in sections below.

Surgery

When possible, surgery is the first line of treatment for any woman with breast cancer, including those who are pregnant. Removing the tumor (lumpectomy) or the entire breast (mastectomy), and/or taking out the lymph nodes under the arm carry little risk to the fetus. But there are certain times in pregnancy when anesthesia (the drugs used to make you sleep for surgery) may be riskier for the fetus. Many doctors, such as the obstetrician, surgeon, and the anesthesiologist will need to work together to decide the best time during pregnancy to do the surgery. If the surgery is done later in the pregnancy, the obstetrician may take part in case there are any problems with the baby during surgery. They can also decide which drugs and techniques are the safest for both the mother and the baby.

Mastectomy can often be used as the first treatment for early stage cancers. Women may also need to have lymph nodes in the armpit taken out, if there is suspicion that the cancer has spread there. Depending on the how far along you are in pregnancy and your cancer stage, your doctor may not want to do a sentinel lymph node biopsy (SNLB). This is when tracers and dye are used to pinpoint the nodes most likely to have cancer cells in early stage breast cancer, which allows removal of fewer nodes. There is concern that the radioactive tracer used for SNLB may affect the fetus if used during times organs are growing quickly. More research is needed on this.

Depending on the cancer's stage, a woman may get more treatment such as chemotherapy, radiation, and/or hormone therapy after surgery to help lower the risk of the cancer coming back (recurrence). This is called adjuvant treatment, since it's used along with the main treatment (surgery).

Women who have breast-saving surgery, like lumpectomy, often need radiation therapy afterward to reduce the chance that the cancer will come back. The need for radiation is an important issue for pregnant women when choosing which surgery to have. Radiation could affect the fetus if given during the pregnancy, so it is not used until after the birth. Doctors don't know how this delay may affect a woman's risk of the cancer coming back. Cancer found in the third trimester may involve very little delay in radiation treatments, so there would likely be no effect on outcome. And a woman who will be getting chemotherapy before radiation may have little or no delay in her radiation treatments. But cancers found early in the pregnancy may mean a longer delay in starting radiation. Treatment must always be considered on a case-by-case basis.

Chemotherapy

Chemotherapy, which is also called "chemo," may be used along with surgery (as an adjuvant treatment) for some earlier stages of breast cancer. It also may be used by itself for more advanced cancers.

Chemo usually is not given during the first 3 months of pregnancy (which is called the first trimester). This is because most of the fetus's internal organs develop during the first trimester. The risk of miscarriage (losing the baby) is also the greatest during the first trimester. The safety of chemo during this time has not been studied because of concerns about damage to the fetus.

It was once thought that all chemo drugs would harm the fetus. But studies have shown that certain chemo drugs used during the second and third trimesters (the fourth through ninth months of pregnancy) do not raise the risk of birth defects or stillbirths. Researchers still do not know whether these children will have any long-term effects.

When a pregnant woman with early breast cancer needs adjuvant chemo after surgery, it is usually delayed until at least the second trimester. If a woman is already in her third trimester when the cancer is found, adjuvant chemo may be delayed until after birth. The birth may be induced (brought on) a few weeks early in these cases. Depending on the extent of the cancer, these same treatment plans may also be used for women whose disease is more advanced.

Chemo should not be given 3 to 4 weeks before delivery. This is because one side effect of chemo is that it lowers the mother's blood counts. This could cause bleeding and increase the chances of infection during birth. Holding off on chemo for the last few weeks before delivery allows the mother's blood counts to return to normal levels before childbirth.

Radiation therapy

Radiation therapy to the breast is often used after breast-conserving surgeries (lumpectomy or partial mastectomy) to reduce the risk of the cancer coming back. The high doses of radiation used for this can harm the fetus any time during pregnancy. It may cause miscarriage, birth defects, or slow fetal growth, so doctors do not recommend its use during pregnancy.

Pregnant women who choose lumpectomy or partial mastectomy can usually have surgery during the pregnancy and wait until after the baby is born to have radiation therapy. But this treatment approach has not been well-studied in pregnant women. And it is not known if the changes that take place in the breasts during pregnancy and the time delay might affect how well the radiation works.

Hormone therapy

Hormone therapy, such as treatment with tamoxifen, may be used as adjuvant treatment after surgery or as treatment for advanced cancer. Its use in pregnant women has not been well-studied, so its effects are not known. Most infants born to women taking tamoxifen are normal. But there have been reports of head and face birth defects in a few babies born to women who became pregnant while taking tamoxifen in early pregnancy. More study in this area is needed.

At this time it is recommended that hormone therapy for breast cancer treatment not be started until after the woman has given birth.

Breast-feeding during cancer treatment

Most doctors recommend that women who have just had babies and are about to be treated for breast cancer should stop (or not start) breast-feeding.

If surgery is planned, stopping breast-feeding will help reduce blood flow to the breasts and make them smaller. This can help with the operation. It also helps reduce the risk of infection in the breast and can help avoid having breast milk collect in biopsy or surgery areas.

Many chemo and hormone therapy drugs can enter breast milk and could be passed on to the baby. So, if the mother is getting chemo or hormone therapy, she shouldn't breast-feed her baby.

If you have specific questions, such as when it might be safe to start breast-feeding, be sure to talk with your health care team. If you plan to start back after you've stopped breast feeding for awhile, you will want to plan ahead. You may need extra help from breast feeding experts.

Pulling all the treatment plans together

The hardest part of treatment is when there is a conflict between the best known treatment for the mother and the well-being of the fetus. A woman who is found to have breast cancer during a pregnancy may have hard choices to make, and she needs to have expert help. Her obstetrician will need to work with her surgeon, her oncologist, her radiation oncologist, and others. Through all this, the woman with breast cancer will need emotional support, so a counselor or psychologist should also be part of her care team.

If you would like more information on breast cancer treatments, look at our document called Breast Cancer.

Effect of pregnancy on survival after breast cancer

Pregnancy before breast cancer

Some studies have found that women who were diagnosed with breast cancer within 2 years after giving birth did not do as well as other women with breast cancer, but other studies have not found such a difference. More research is needed in this area.

Pregnancy during breast cancer

Pregnancy may make it harder to find, diagnose, and treat breast cancer. But most studies have found that the outcomes among pregnant and non-pregnant women with breast cancer is about the same for cancers found at the same stage. For example, a study at Memorial Sloan-Kettering Cancer Center showed that pregnant women who had a mastectomy did no worse than women who were not pregnant and had a mastectomy. Survival rates after 5 and 10 years were almost the same in these 2 groups. So pregnancy and the breast changes it causes did not worsen the mother's chances of surviving breast cancer.

Some doctors believe that ending the pregnancy may help slow the course of more advanced breast cancers, and they may recommend an abortion in these cases. It has been hard to prove whether this improves the women's outcomes. It is hard to do research in this area and very few good studies have been done. The studies that have been done have not shown that ending the pregnancy improves a woman's survival or cancer outcome.

Studies have not shown that the treatment delays sometimes needed during pregnancy have an effect on breast cancer outcome. But this, too, has proven to be a difficult area to study.

Pregnancy after breast cancer treatment

Some treatments for breast cancer, such as certain chemo drugs, may affect a woman's ability to have a baby (fertility). Still, many women are able to become pregnant after treatment. Women concerned about their fertility should talk to their doctors about this before starting breast cancer treatment.

Doctors are not sure if women who have had breast cancer in the past increase their risk of the cancer coming back by becoming pregnant. A few studies have been done on this. Most have found that pregnancy does not increase the risk of the cancer coming back after successful treatment of breast cancer.

But doctors know there is a clear link between estrogen levels and growth of breast cancer cells. Because of this link, many doctors advise breast cancer survivors to wait at least 2 years after treatment before trying to get pregnant, though the best length of time to wait is not clear. Two years is thought to give them the chance to find any early return of the cancer, which could affect a woman's decision to become pregnant later on. Still, this advice is not based on data from any clinical trials. Other studies point out that breast cancer can come back after the 2 year mark, so every case is different. Each woman's decision is based on many things, such as her age, fertility, desire for more pregnancies, type of breast cancer, risk of an early relapse, and the potential effect estrogen may have on her risk of a breast cancer coming back.

Women taking hormone therapy, such as tamoxifen, should talk with their doctors before trying to become pregnant. These drugs could affect a growing fetus (see the section, "Hormone therapy").

There is no proof that a woman's past breast cancer has any direct effect on her baby. But women who have had breast radiation should know that they may have problems breast feeding.

Another important thing to remember is that chemotherapy for breast cancer can damage the ovaries, sometimes causing immediate or delayed infertility. Cancer treatment can also cause women to delay trying to get pregnant. These factors together often mean that a woman has less of a chance of getting pregnant after breast cancer treatment. For more information about how cancer treatment can affect fertility, see our document Fertility and Cancer: What Are my Options?

All women who have had breast cancer and are thinking about having children should talk with their doctors about how the treatment they got can affect their chances for pregnancy. They will also want to know their risk of cancer coming back. In many cases, counseling can help women sort through the choices that come with surviving breast cancer and planning a pregnancy.