Breast cancer can occur during pregnancy or shortly after childbirth. While not common in this age group, this diagnosis is significant enough to have its own classification. Awareness of this possibility and the unique challenges it presents is important for both patients and healthcare providers.
Defining Pregnancy-Associated Breast Cancer
Pregnancy-Associated Breast Cancer (PABC) refers to breast cancer diagnosed during pregnancy or within the first year after delivery. This diagnosis occurs in approximately one in every 3,000 to 10,000 pregnancies, making it relatively rare. PABC accounts for nearly seven percent of all breast cancers diagnosed in women under the age of 45.
The incidence of PABC is projected to rise as more women choose to delay childbearing, since age is a known risk factor for breast cancer. The hormonal environment of pregnancy may affect the cancer’s biology, sometimes leading to more aggressive tumor characteristics. PABC cases are more frequently found to be triple-negative or HER2-positive, which are subtypes often associated with a less favorable outlook.
Some research suggests that the involution process of the breast after breastfeeding, which involves tissue remodeling and inflammation, may promote tumor growth in the postpartum period. This has led some experts to suggest expanding the definition of PABC to include diagnoses up to five years postpartum due to an increased risk of metastasis and mortality. The majority of PABC cases are diagnosed after the baby is born, often within the first six months postpartum.
Challenges in Detection and Diagnosis
Detecting breast cancer during pregnancy is difficult due to the significant physiological changes the breast undergoes. Hormonal shifts cause the breast tissue to swell, become tender, and increase in density, which can mask a small lump. This natural lumpiness and swelling can lead both the patient and the physician to mistake a cancerous mass for a normal pregnancy-related change, causing a delay in diagnosis.
When a suspicious lump is found, the initial diagnostic tool is typically a breast ultrasound, which uses sound waves and is safe for the fetus. Ultrasound determines if a mass is a fluid-filled cyst or a solid tumor, providing a first step in the investigation. If the mass is solid, a mammogram is often performed to get a detailed image of the tissue.
Mammography is considered safe during pregnancy because it uses a low dose of radiation. A lead shield is placed over the abdomen during the procedure for fetal protection. Should imaging tests suggest a concerning mass, a core needle biopsy is the standard next step, using only local anesthesia. Other imaging tests, such as CT scans and bone scans, are avoided due to higher radiation exposure. MRI with gadolinium contrast is contraindicated because the contrast agent can cross the placenta.
Navigating Treatment Options During Pregnancy
Treating breast cancer while pregnant requires careful coordination to prioritize both the mother’s health and the developing fetus. Treatment protocols are modified based on gestational age. Surgery is generally considered a safe and primary treatment option at any point during pregnancy.
A modified radical mastectomy, which removes the entire breast, is often the preferred surgical choice if the diagnosis is made early in the pregnancy. This is because breast-conserving surgery, or lumpectomy, typically requires follow-up radiation therapy, which is not safe for the fetus. If the cancer is diagnosed later in the pregnancy, a lumpectomy may be an option, with radiation delayed until after delivery.
Chemotherapy is considered safe for the fetus when administered during the second and third trimesters, after the major period of organ development is complete. It is strictly avoided during the first trimester due to the risk of birth defects. Certain types of chemotherapy, such as anthracycline-based regimens, have been shown to be safe for use in the later stages of pregnancy.
Targeted therapies, such as trastuzumab for HER2-positive cancers, and hormonal therapies, including tamoxifen, are generally contraindicated. These systemic treatments can cross the placenta and potentially harm the fetus. They must be delayed until after the baby is born.
Radiation therapy, which uses high-energy beams to kill cancer cells, is generally postponed until after delivery because of the risk of radiation exposure to the fetus, which can cause complications.
Prognosis and Postpartum Considerations
The prognosis for PABC patients compared to non-pregnant patients is often debated, but many studies suggest a less favorable outcome, primarily because the diagnosis is often made at a later, more advanced stage. When PABC is matched with non-PABC cases by age, stage, and tumor biology, the long-term survival rates can be similar. However, the frequent delay in diagnosis means PABC is more often associated with larger tumors and greater lymph node involvement.
For patients who require ongoing systemic treatment after delivery, such as chemotherapy, hormonal therapy, or targeted therapy, breastfeeding must generally be avoided. The medications can pass into the breast milk and pose a risk to the infant. Milk suppression techniques may be necessary if the mother must start these treatments immediately postpartum.
The long-term follow-up and monitoring for PABC patients after treatment are the same as for other breast cancer survivors. Although there may be concerns about future pregnancies, current evidence suggests that a subsequent pregnancy does not negatively affect the breast cancer prognosis. Women who have completed their treatment and wish to become pregnant should discuss their plans with their oncology team.