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Breast Cancer and Pregnancy

Most lumps, nipple discharges, and other worrisome breast changes discovered during pregnancy are not cancerous. Breast abnormalities during pregnancy can be caused by many of the same processes seen in non-pregnant women or from benign changes to the breast tissue that occur during pregnancy and lactation (breast-feeding). However, breast cancer can occur during pregnancy and is actually diagnosed more frequently in pregnant women than in non-pregnant women of the same age. Breast cancer occurs in one in 3,000 (0.03%) to one in 10,000 (0.01%) of all pregnant women. Breast cancer during pregnancy is diagnosed in greater numbers in women who delay childbearing until their later 30s or early 40s. This is due primarily to the fact that the risk of breast cancer increases with age.

Breast Changes During Pregnancy and Lactation (Breast-Feeding)

During pregnancy, increased levels of the hormones estrogen and progesterone stimulate a variety of breast changes. Typically, the breasts become tender and the nipples become sore a few weeks after conception. The Montgomery’s gland surrounding the areola (the pigmented region around the nipple) becomes darker and more prominent, and the areola itself darkens.

One of the most common changes stimulated by the hormones of pregnancy is a rapid period of breast growth, especially during the first eight weeks of pregnancy. In fact, it is not uncommon for a woman’s breasts to increase by one or two cup sizes during pregnancy and lactation. This rapid growth is due to anatomic changes in the breast tissue that include expansion of the blood vessels and fluid retention within the breasts. In addition, estrogens stimulate the growth of the breast ducts and surges of progesterone cause the glandular tissue to expand.

It is not uncommon for the breasts to increase by one to two bra cup sizes during and pregnancy and lactation. The breasts usually return to their previous size, or slightly smaller, after breast-feeding is completed.

Later in the first trimester of pregnancy, levels of the two hormones responsible for milk production, prolactin and oxytocin, begin to increase. Prolactin is sometimes referred to as the "mothering hormone" because some people believe it also causes a tranquilizing effect that makes women feel more maternal. The body begins producing prolactin approximately eight weeks after conception. As the pregnancy progresses, the levels of prolactin steadily increase, peaking when the woman gives birth. As the body produces more and more prolactin, high levels of estrogen and progesterone block some of the prolactin receptors and inhibit milk production until after the baby is born.

After birth, estrogen and progesterone levels decrease and the production of prolactin declines. The breasts will usually begin to produce milk three to five days after a woman has given birth. During these few days before milk is produced, the breasts secrete colostrum, a liquid substance that contains antibodies to help protect the infant against infections. Some physicians believe that colostrum also decreases an infant's chances of developing asthma and other allergies. Within a few days, the infant’s need for high levels of the maternal antibodies in the colostrum decreases. At about the same time, the breasts begin to produce milk, which contains lower levels of antibodies that are passed on to the infant during breast-feeding. These antibodies are believed to decrease the infant’s susceptibility to disease and infections in early life.

The other hormone responsible for milk production, oxytocin, triggers the delivery of milk that prolactin has produced. When an infant suckles at the mother’s breast, milk is actively drawn out of the nipples by the suckling action and passively delivered to the infant by the contraction of small muscles surrounding the ducts in the breast. This process is commonly called the let-down reflex. The infant’s suction signals the body to produce more milk (using prolactin) and deliver more milk (using oxytocin). A variety of other hormones that stimulate growth and development in the infant are also delivered in the breast milk, including insulin, thyroid, and cortisol.

A woman’s body continues to produce milk until she stops breast-feeding or mechanically pumping breast milk. Even then, it may take several months for milk production to completely stop. The breasts usually return to their previous size, or slightly smaller, after breast-feeding is completed.

Breast Health Guidelines During Pregnancy

A woman should continue practicing monthly breast self-exams during pregnancy at about seven to 10 days after her normal period would have occurred. It is especially important that a clinical breast exam be performed by the physician or nurse during the first doctor’s appointment of the pregnancy, before the breasts go through significant physiologic changes. Some changes or lumps are more difficult to evaluate once the breasts have enlarged and have become more nodular. Clinical breast exams should continue on a monthly basis during pregnancy.

A main concern with breast cancer during pregnancy is a delay in the detection of a breast abnormality. The changes that occur during pregnancy may make cancers more difficult to diagnose and may result in a woman being diagnosed with breast cancer at a more advanced stage, when the chances of successful treatment and survival are lower. Vigilant monthly breast self-exams and clinical breast exams during pregnancy and lactation (breast-feeding) can help prevent the delayed diagnosis of breast cancer and enable optimal treatment.

Screening mammograms in asymptomatic women (women who have no symptoms of breast cancer) are not performed during pregnancy or lactation and may be performed at a later time. However, if a breast abnormality (such as a strange lump) is detected during pregnancy, a diagnostic mammogram and/or ultrasound (sonogram) may be performed. A diagnostic mammogram involves taking x-rays of the breast from special angles and/or using special magnification. Mammography uses a very low dose of radiation and is considered safe for the fetus if there is a medical need for the exam. A lead apron is usually placed over the woman’s stomach/abdomen area during the mammogram to shield the developing fetus.

Vigilant monthly breast self-exams and clinical breast exams during pregnancy and lactation (breast-feeding) can help prevent the delayed diagnosis of breast cancer and enable optimal treatment.

Evaluating a Breast Abnormality During Pregnancy

The hormonal changes during pregnancy and lactation (breast-feeding) may influence the growth of estrogen-sensitive tumors. Non-cancerous tumors are common during pregnancy and their growth may be stimulated by increased hormone levels. However, all breast lumps and abnormalities should be evaluated by a physician to distinguish between the more common benign changes and the potentially malignant (cancerous) ones.

Non-cancerous conditions that are common during pregnancy include:

  • Cysts (collections of fluid)
  • Galactoceles (milk-filled cysts)
  • Fibroadenomas (tumors; existing ones may enlarge during pregnancy)

It is fairly common for the nipples to discharge small amounts of milky, clear, or sometimes bloody fluid during pregnancy and lactation. During pregnancy and lactation, breast tissue grows rapidly. Rapid tissue growth can lead to irritation of the breast ducts, causing nipple discharge. This discharge, whether blood or other fluid, is usually related to a non-cancerous condition, such as shedding of the cells lining the breast ducts or a papilloma (a benign wart-like growth). However, patients should consult their physicians if they experience nipple discharge to determine whether the discharge requires further examination.

If a breast abnormality or lump is detected during pregnancy, it should be presented immediately to a physician who will conduct a thorough clinical breast exam. The physician may also order an ultrasound (sonogram) exam and/or mammogram. Ultrasound is excellent at distinguishing cysts and is routinely used for fetal imaging because it does not harm the fetus. Mammography, with proper shielding, is also considered safe for a pregnant woman and her fetus. Mammography uses a very low level of radiation and should not be delayed if deemed necessary.

In many cases, a non-surgical biopsy will be performed if a suspicious breast lump or abnormality is detected in a pregnant woman. A biopsy helps determine whether a breast mass is cancerous or benign. Fine needle aspiration biopsy (FNA) involves using a thin needle to drain fluid or sample cells from the breast. FNA is often used to identify and drain cysts or remove cells for microscopic examination. Other methods of breast biopsy that use larger needles than FNA, such as core needle biopsy or vacuum-assisted biopsy, can also be performed safely during pregnancy if they are warranted. In some cases, an open surgical biopsy may be necessary to diagnose a breast mass. If so, careful planning can help reduce any risks to the mother and fetus.