Breast Cancer During Pregnancy: A Comprehensive Guide to Diagnosis, Treatment, and Safety for Mother and Baby

Table of Contents

• Key Points
• Introduction: Why This Research Matters
• How Common Is Breast Cancer During Pregnancy?
• Recognizing Symptoms During Pregnancy
• Diagnosis: Examining the Breast (Local Staging)
• Diagnosis: Checking for Cancer Spread (Distant Staging)
• Understanding Radiation Risks and Doses
• Tumor Types and Biological Characteristics
• Genetic Findings in Pregnancy-Associated Breast Cancer
• Treatment Overview: Balancing Mother and Baby
• Surgery During Pregnancy
• Sentinel Lymph Node Biopsy: Checking for Lymph Node Spread
• Clinical Implications: What This Means for Patients
• Limitations of This Research
• Recommendations for Patients
• Frequently Asked Questions
• Source Information

Key Points

• Most women with breast cancer during pregnancy can safely continue pregnancy while receiving treatment, including surgery and chemotherapy after the first trimester.
• In a large international study, 88% of singleton pregnancies resulted in live birth, but 48% delivered preterm and chemotherapy was linked to more fetal complications.
• Termination of pregnancy has not been shown to improve breast cancer outcomes; avoiding treatment delays can reduce risks from premature birth.
• Pregnant patients more often have aggressive tumor types like triple-negative breast cancer, but treatment follows standard guidelines based on each tumor's biology.
• Specialized multidisciplinary care is essential; endocrine therapy and HER2-targeted therapy are not used during pregnancy, and children exposed to treatment need long-term follow-up.

Introduction: Why This Research Matters

Finding out you have breast cancer while pregnant is a frightening and overwhelming experience. The good news is that medical knowledge in this area has advanced significantly. This review article, published in Best Practice & Research Clinical Obstetrics and Gynaecology, was written by a team of European specialists including medical oncologists, gynecological oncologists, radiation oncologists, surgical oncologists, obstetricians, and pediatric oncologists. They came together to summarize the most current evidence on how to diagnose and treat breast cancer during pregnancy.

The guiding principle is clear: women should receive state-of-the-art cancer treatment without unnecessary delay, and the pregnancy should be maintained as long as possible—provided it is safe to do so. Treatment decisions should be made by a multidisciplinary team that carefully weighs the selection, sequence, and timing of treatments based on patient factors, tumor characteristics, pregnancy stage, and the patient's own preferences.

One of the most important messages from this research is that starting cancer treatment during pregnancy often reduces the risks of early delivery and prematurity. In other words, treating cancer while pregnant can actually protect the baby by allowing the pregnancy to continue closer to full term. The article also describes how specialized teams, such as the multidisciplinary Advisory Board for Cancer in Pregnancy founded in the Netherlands in 2012, can help clinicians make individualized recommendations. These virtual tumor boards include cancer surgeons, gynecological oncologists, obstetric medicine experts, fertility specialists, radiation oncologists, medical oncologists, hematologists, pediatric oncologists, imaging specialists, clinical pharmacologists, and ethicists.

How Common Is Breast Cancer During Pregnancy?

Cancer during pregnancy is rare, occurring in approximately 1 in 1,000 pregnancies. Among all cancers diagnosed during pregnancy, breast cancer is the most frequent. PrBC is found in 1 in 3,000 to 10,000 women, which corresponds to about 2,000 to 4,000 pregnant women in Europe each year.

The incidence is likely to rise for two reasons. First, more women are delaying pregnancy to more advanced maternal ages, which increases the background risk of cancer. Second, the wider use of genome-wide non-invasive prenatal testing for fetal chromosome screening will likely lead to incidental discovery of maternal cancers during pregnancy.

In a large cohort study from the International Network on Cancer, Infertility and Pregnancy (INCIP) that included 1,170 patients over a 20-year period, researchers found that 67% of patients received cancer treatment during pregnancy, and the likelihood of receiving treatment during pregnancy increased over time—mainly due to increased use of chemotherapy. Overall, 955 (88%) of 1,089 singleton pregnancies resulted in a live birth, of which 48% were delivered preterm. Over the years, there were more live births and fewer medically induced (iatrogenic) preterm deliveries.

However, the study also found that exposure to chemotherapy before birth was associated with more fetal complications—specifically, babies who were small for gestational age (smaller than expected for their stage of development) and more frequent admissions to the neonatal intensive care unit (NICU). These findings highlight why careful monitoring and specialized care are essential.

To put breast cancer in younger women in context: among adolescents and young adults (AYA) between ages 15 and 39, breast cancer is the most common cancer diagnosis, with an age-adjusted rate of 22.9 new cases per 100,000 female AYAs and an age-adjusted death rate of 2.2 per 100,000 female AYAs. Approximately 0.2% to 2.6% of all breast cancers occur during pregnancy, while 35% to 55% of all cases in women under age 45 occur within 5 to 10 years after pregnancy.

It is worth clarifying the terminology used in research. The terms "pregnancy-associated breast cancer" (PABC) and "breast cancer during pregnancy" (PrBC) have historically been used inconsistently. PABC often includes both cancer diagnosed during pregnancy and cancer diagnosed within 6 months to 1 year after delivery. More recently, experts recommend separating these conditions, with postpartum breast cancer (PPBC) potentially extending to 5 to 10 years after birth, as the biology may differ.

Recognizing Symptoms During Pregnancy

Pregnant patients with breast cancer may experience the same symptoms as non-pregnant women, such as a palpable lump or nipple discharge. However, there is often a delay in diagnosis because pregnancy causes natural changes in the breasts—including engorgement (swelling from increased blood flow), hypertrophy (enlargement), nipple discharge, and increased density of breast tissue. These normal changes can mask or mimic cancer symptoms.

Because of this delay, women may present with more advanced disease stages at the time of diagnosis. This is a critical reason why the authors emphasize that any suspicious or palpable breast mass that persists for 2 weeks or more during pregnancy should be investigated—even though 80% of breast lesions during pregnancy turn out to be benign.

Diagnosis: Examining the Breast (Local Staging)

When a pregnant woman has a palpable breast mass, the diagnostic workup includes clinical examination, imaging, and biopsy. The medical team will assess the disease stage according to the American Joint Committee on Cancer (AJCC) tumor, node, and metastasis (TNM) staging system.

Breast ultrasound—including examination of the axillary (underarm) area—is the first imaging method of choice. It does not involve ionizing radiation, making it completely safe for the fetus. It also allows for immediate identification of obvious benign lesions such as cysts and galactoceles (milk-filled cysts), which require no further evaluation. When suspicious lesions are found, a biopsy can be performed using ultrasound guidance. The combined sensitivity (ability to correctly identify cancer) and specificity (ability to correctly identify non-cancer) for detecting malignancy during pregnancy are 80.1% and 88.4%, respectively, meaning the test correctly identifies cancer in about 4 out of 5 cancer cases and correctly rules it out in nearly 9 out of 10 non-cancer cases.

Mammography may also be performed, with either one mediolateral oblique (MLO) view or two views (MLO plus craniocaudal). When ultrasound is combined with mammography using craniocaudal and MLO views of both breasts, doctors can better assess tumor extent, multifocality (multiple tumors in one breast), or bilateral disease (cancer in both breasts). The incremental detection rate of this combined approach is comparable to that of contrast-enhanced breast MRI, finding additional cancers in 15.5% of cases in the ipsilateral breast (same breast as the known tumor) and 3.9% in the contralateral breast (opposite breast).

Ultrasound is also used to assess regional lymph node status. Suspicious lymph nodes can be confirmed by fine-needle aspiration or biopsy. Because of the effectiveness of ultrasound plus mammography, contrast-enhanced breast MRI can generally be omitted during pregnancy.

Outside of pregnancy, contrast-enhanced MRI is often used for women with BRCA gene mutations, lobular cancer, dense breast tissue, suspected multicentricity or multifocality, before neoadjuvant (pre-surgical) therapy, or when other imaging results are inconclusive. However, the use of gadolinium-based contrast agents (the "dye" used in MRI) is controversial during pregnancy. Although there are no known birth defect (teratogenic) effects of gadolinium-based contrast agents in humans, the U.S. Food and Drug Administration (FDA) categorizes them as pregnancy category C, meaning risk cannot be ruled out. Gadolinium crosses the placenta and enters fetal circulation. After excretion through the fetal urine, small amounts remaining in the amniotic fluid may break down into potentially toxic free gadolinium ions, with unclear long-term effects on the fetus. Therefore, contrast-enhanced MRI during pregnancy should only be performed when it will change clinical decision-making AND cannot be postponed until after delivery. If it is necessary, the lowest possible dose should be used.

Diagnosis: Checking for Cancer Spread (Distant Staging)

Just as in non-pregnant women, further staging (checking whether cancer has spread to other parts of the body) should only be performed in high-risk early breast cancer cases. This includes situations where there are clinically positive axillary lymph nodes, large tumors (5 cm or larger), aggressive tumor biology, or clinical signs, symptoms, or laboratory values suggesting metastatic disease. In these cases, doctors consider a chest CT scan, abdominal imaging, and a bone scan.

PET/CT scans (positron emission tomography combined with computed tomography) may replace traditional imaging in some cases, but they can be less sensitive for lobular cancers and low-grade tumors.

During pregnancy, ultrasound and MRI are strongly preferred for staging because they do not use ionizing radiation and perform accurately. CT and PET/CT scans can be selectively performed during pregnancy when the benefit to the mother outweighs the risk to the fetus—specifically, when results will change clinical management AND cannot be postponed until after pregnancy. When these scans are necessary, radiation doses should be kept as low as reasonably achievable, and cumulative fetal radiation exposure over 100 mGy should be avoided.

A newer technique called whole-body diffusion-weighted MRI can be used for staging when available. Recent studies show excellent diagnostic performance for detecting distant metastases (including in bone, liver, and peritoneum/abdominal lining) as well as lymph node metastases in pregnant cancer patients. Studies demonstrated high inter-reader agreement, 90% accuracy for primary tumor detection, 98.5% to 99.5% accuracy for detecting lymph node metastases, and 90% to 100% accuracy for detecting distant metastases.

Understanding Radiation Risks and Doses

Fetal exposure to ionizing radiation and its related risks depend on four factors: gestational age, radiation dose, exposure time, and the type of nuclide used (if applicable). The influence of radiation on pregnancy varies by timing: radiation can cause fetal death in the first 2 weeks after conception, malformations up to 2 months, and decreased IQ between the 3rd and 6th month of pregnancy.

Radiation effects are divided into two categories. Deterministic effects—such as miscarriage, growth restriction, congenital malformations, microcephaly (abnormally small head), or impaired fetal development—occur when fetal exposure exceeds a threshold dose of 100 to 200 mGy. From 8 to 15 weeks of gestation, the fetus is most susceptible to radiation-induced mental retardation, with a reduction of 21 IQ points per 1,000 mGy above a threshold of about 50 mGy. From 16 to 25 weeks, the reduction is 13 IQ points per 100 mGy above the same threshold of about 50 mGy. After 25 weeks, no clear relationship has been described.

Reassuringly, radiation doses delivered from routine diagnostic exams are up to 100 times lower than these danger thresholds. However, extra caution is needed when multiple imaging studies are required, to ensure the cumulative fetal radiation dose does not inadvertently exceed safe limits.

Stochastic effects are random, unpredictable cancer-causing (oncogenic) or mutation-causing (mutagenic) effects of radiation that have no safe threshold. The carcinogenic risk appears highest during the first trimester. A fetal exposure of 10 to 20 mGy may increase the background risk of childhood leukemia by a factor of 1.5 to 2.0, compared to a background rate of approximately 1 in 3,000 children. Importantly, only direct exposure within the radiation field adds to fetal risk—indirect fetal exposure from scattered radiation is negligible. This means abdominal shielding during radiography or CT is not necessary, and it might even increase internal scatter radiation.

Here are the typical fetal radiation doses for various imaging tests, compared to the annual background radiation of 1.1 to 2.5 mGy that everyone receives from natural sources:

• Chest X-ray: less than 0.01 mGy
• Mammography (two planes, bilateral): 0.001 to 0.01 mGy
• CT of the head: less than 0.005 to 0.5 mGy
• CT of the chest: less than 0.01 to 0.66 mGy
• CT of the abdomen: 1.3 to 35 mGy
• CT of the pelvis: 10 to 50 mGy
• Low-dose perfusion scintigraphy: 0.1 to 0.5 mGy
• 99mTc-bone scintigraphy: 3.3 mGy
• 18F-FDG PET whole-body scintigraphy: 1.1 to 990 mGy
• 18F-FDG PET/CT whole-body scintigraphy: 10 to 50 mGy
• 18F-FDG PET/MRI whole-body scintigraphy: 3.334 mGy

Note that actual radiation doses may vary depending on the imaging device and technique used, and doses have decreased over recent decades for many imaging modalities. Fetal exposure during nuclear studies also depends on the physical and biochemical properties of the nuclide used.

In nuclear imaging, the two most commonly used tracers—18F-fluorodeoxyglucose (FDG) and technetium (Tc-99m)—can be used safely in pregnant patients. Several measures can minimize fetal radiation dose during nuclear imaging:

• Careful dose calculation that accounts for physiological pregnancy changes
• Use of a bladder catheter along with intravenous hydration to avoid accumulation of the tracer in the maternal bladder
• Adjustment of scanning time

However, standard use of hybrid imaging with CT will increase cumulative fetal radiation exposure. As an alternative, PET/MRI is a promising new development with improved detection of distant metastases compared to PET/CT. So far, this technique has been studied in only a small series of pregnant cancer patients, but it results in a very low fetal radiation dose (3.3 mGy).

Tumor Types and Biological Characteristics

Pathological diagnosis should be based on a core needle biopsy, classified according to the World Health Organization (WHO) classification and the AJCC TNM staging system. Breast cancer is classified into stages 0 through IV, which helps doctors determine prognosis and potential treatment approaches. Staging incorporates information about tumor biology, including tumor grade, estrogen receptor (ER) status, progesterone receptor (PR) status, human epidermal growth factor receptor 2 (HER2) status, Ki-67 (a marker of cell proliferation), and gene expression data when applicable.

Gene expression analysis can categorize breast cancer into four main biological subtypes:

• Luminal A: ER positive, PR positive, HER2 negative, low Ki-67
• Luminal B: ER positive, PR positive, HER2 negative OR HER2 positive, high Ki-67
• HER2-enriched: ER negative, PR negative, HER2 positive
• Basal-like (triple-negative): ER negative, PR negative, HER2 negative

PrBC is similar to the phenotypes most commonly found in young breast cancer patients in general. These tumors are mainly high-grade invasive carcinomas not otherwise specified (NOS), often with aggressive characteristics: larger tumors, a higher incidence of positive lymph nodes, and lymphovascular invasion (cancer cells in blood or lymph vessels).

A large, recently published cohort derived from two registries—the INCIP registry and the German Breast Group (GBG)—compared 662 pregnant patients to 1,082 non-pregnant cancer patients aged up to 45 years. The findings were striking. Pregnant patients were more likely to have:

• Stage II breast cancer: 60.1% vs. 56.1% (p = 0.035, statistically significant)
• Grade 3 tumors: 74.0% vs. 62.2% (p < 0.001, highly significant)
• Hormone receptor-negative tumors: 48.4% vs. 34.0% (p < 0.001)
• Triple-negative breast cancer (TNBC): 38.9% vs. 26.9% (p < 0.001)

HER2 positivity was found in 29.2% of pregnant patients, a difference that was not statistically significant compared to non-pregnant patients. A more detailed comparison of tumor characteristics between pregnant and non-pregnant patients (with updated numbers from additional data) shows:

• Median age: 34 years (range 22–47) in pregnant patients vs. 38 years (range 19–45) in non-pregnant patients
• Stage I: 15.4% (16.1% in updated data) vs. 30.4% (20.9%)
• Stage II: 56.9% (60.1%) vs. 46.1% (56.1%)*
• Stage III: 27.7% (23.8%) vs. 23.5% (23.0%)
• Grade 1–2: 23.8% (26.0%) vs. 43.5% (35.8%)
• Grade 3: 76.2% (74.0%) vs. 56% (62.2%)**
• Non-lobular histology: 97.4% (96.6%) vs. 91% (94.6%)
• Invasive lobular histology: 2.6% (3.1%) vs. 9% (5.4%)
• ER and/or PR positive: 46.6% (51.6%) vs. 74.5% (66.6%)**
• HER2 positive: 31.8% (29.2%) vs. 17% (27.2%)
• Triple negative: 37.9% (38.9%) vs. 19.1% (26.9%)**

*p = 0.035; **p < 0.001

When examining biological subtypes specifically, pregnant patients consistently have less luminal A disease and more basal-like/triple-negative disease compared to non-pregnant patients:

• Luminal A: 10.8%–13.7% in pregnant vs. 24.0%–50.9% in non-pregnant
• Luminal B: 18.2%–38.4% vs. 20.1%–21.1%
• HER2 positive: 15.8%–29.2% vs. 8.0%–27.2%
• Basal-like/TNBC: 30.1%–38.9% vs. 17.4%–26.9%

Genetic Findings in Pregnancy-Associated Breast Cancer

The most commonly mutated genes in breast cancer patients are TP53 and PIK3CA, with no significant differences between pregnant and non-pregnant breast cancer patients. However, there are molecular differences in PrBC compared to non-pregnancy-related breast cancer, including a higher frequency of mutations in the mucin gene family and an enrichment of mismatch repair deficiency mutational signature (a type of genetic instability). The mucin gene family plays a major role in glycosylation mechanisms—the process of attaching sugar molecules to proteins—and alterations in glycosylation are correlated with breast cancer development and spread.

A recent systematic review summarized available data on the genomic background and gene mutation patterns of pregnancy-associated breast cancer compared to non-pregnant patients. The research found aberrant expression of several oncogenes (cancer-promoting genes) including MYC, FOS, and MUC1, as well as altered expression of apoptosis regulators (genes that control programmed cell death), transcription regulators, DNA repair genes (such as Sig20 and BRCA1), cell proliferation genes (IGF1 and MKI67), immune response genes (PD1 and PDL1), and other biological processes. In contrast, the most down-regulated (suppressed) genes were tumor suppressor genes (TP53 and PTEN), cell cycle regulator genes (BCL2), DNA repair genes, and genes involved in protein modification and transport.

Researchers hypothesize that these features may promote tumor progression during pregnancy or the postpartum period, with distinct differences between PrBC (cancer during pregnancy) and PPBC (postpartum breast cancer).

Genetic counseling is especially important for women diagnosed with breast cancer during pregnancy. Women with a BRCA1 germline mutation appear to have an increased risk of developing PrBC. In one study of 20 women with pregnancy-associated breast cancer using a 94-cancer gene panel, 7 women carried pathogenic (disease-causing) mutations in BRCA1 or CHEK2. Because of their young age at diagnosis and the clinical consequences, all women with PrBC should be referred for genetic counseling.

Treatment Overview: Balancing Mother and Baby

The goal of treatment during pregnancy is straightforward: achieve the best possible oncological outcome for the mother while protecting the fetus. Whenever possible, physicians should follow the same standard-of-care treatment guidelines used for non-pregnant patients. Decisions about treatment are guided by patient and tumor characteristics, cancer stage, gestational age, and the wishes of the patient and her partner regarding continuation of the pregnancy.

It is essential to establish early on whether treatment is curative or palliative in intent, as this affects all subsequent decisions, including those about continuing the pregnancy. A multidisciplinary team should assess and weigh the medical (obstetrical), oncological, radiotherapeutic, pediatric, molecular/genetic, ethical, and psychological issues. The patient and her partner need careful counseling about treatment options, maternal and fetal risks, and decisions concerning continuation or termination of the pregnancy.

A crucial finding from the research is that termination of pregnancy has NOT been shown to improve maternal outcomes for breast cancer. Therefore, premature delivery or unnecessary delay in diagnosis or treatment—just to start treatment after birth—should be avoided. Prematurity can often be minimized by starting cancer treatment during pregnancy.

Here is how each major treatment modality fits into pregnancy:

• Surgery: Possible during all trimesters
• Radiotherapy: Possible during the first half of pregnancy
• Chemotherapy: Can be safely administered starting from 12 weeks of gestational age (after the first trimester, when the baby's organs are formed)
• Endocrine therapy (hormone-blocking treatments like tamoxifen or aromatase inhibitors): Contraindicated throughout the entire pregnancy
• HER2-targeted therapy (such as trastuzumab): Contraindicated throughout the entire pregnancy

Importantly, fetal growth should be monitored regularly during cancer treatment, and long-term follow-up of the children is encouraged in dedicated centers.

Surgery During Pregnancy

Breast cancer surgery can be performed safely during any stage of pregnancy. Currently used anesthetics at standard concentrations are not known to have any birth defect (teratogenic) effects. The passage of anesthetic medication through the placenta depends on its lipophilicity (fat solubility), degree of ionization, molecular mass, and protein binding. The timing of surgery should be based on patient and tumor characteristics, gestational age, and patient preferences. Elective (non-urgent) surgery should be postponed until after delivery.

In general, risks of surgery during pregnancy include preterm delivery, miscarriage, and fetal distress. However, in non-abdominal surgery (which breast surgery is), these risks are small. Adequate maternal care during the perioperative period is the most important factor for fetal well-being. After 20 weeks of gestation, the patient should be positioned in a left lateral tilt to ensure optimal blood flow through the vena cava (the large vein returning blood to the heart).

Certain conditions must be actively prevented because they can harm fetal health and development: hypoxia (low oxygen), hypotension (low blood pressure), hypoglycemia (low blood sugar), fever, pain, infections, and thrombosis (blood clots). Placental perfusion (blood flow) is determined primarily by maternal blood pressure and lacks autoregulation—meaning that if the mother's blood pressure drops due to hemorrhage or low blood volume, placental blood flow decreases and the fetus can become缺氧 (oxygen-deprived).

Monitoring of fetal heart rate (FHR) by cardiotocography (CTG) during surgery is debatable but can be useful to detect fetal distress, depending on gestational age and potential viability (whether the baby could survive if delivered early). If fetal monitoring is used, it is recommended to perform surgery at an institution with neonatal and pediatric services, and to have an obstetric care provider readily available. Obstetricians should be aware that fetal heart rate patterns will be influenced by anesthesia and surgery. Nonetheless, CTG before and after a procedure is a minimum requirement. If there are signs of fetal distress, staff should consider repositioning the patient, and providing fluid replacement and oxygen.

Other perioperative measures include pain medication (since excessive pain may trigger preterm labor) and appropriate thromboprophylaxis with low molecular weight heparin (LMWH) to reduce the risk of venous thromboembolic events (blood clots in veins).

Regarding the type of breast surgery, the choice during pregnancy should follow the same guidelines as for non-pregnant women, favoring breast-conserving therapy when feasible. If immediate breast reconstruction is considered, prosthetic implants are possible, but autologous reconstruction (using the patient's own tissue) should be delayed until after delivery, taking physiological changes into account. Importantly, the need for radiotherapy after breast-conserving surgery should not be used as an argument to favor mastectomy, because radiotherapy can safely start after delivery.

The following medications can be used safely during and after surgery:

• Anesthetics: Desflurane, Propofol
• Pain medications: Opiates including sufentanil (maximum 30 mg) and morphine; Lidocaine; Ketamine
• Anti-nausea medications: Ondansetron, metoclopramide, granisetron
• Steroids: Hydrocortisone, methylprednisolone, prednisolone, dexamethasone (note: methylprednisolone, hydrocortisone, and prednisolone are preferred because they are metabolized in the placenta, leading to lower concentrations in the fetus)
• Stomach acid reducers: Proton pump inhibitors

Discouraged medications include: NSAIDs (non-steroidal anti-inflammatory drugs, except when used specifically as anti-tocolytic agents to stop preterm labor) and Metamizole (an analgesic not recommended in pregnancy).

Sentinel Lymph Node Biopsy: Checking for Lymph Node Spread

Sentinel lymph node staging—the procedure used to determine whether cancer has spread to the first (sentinel) lymph node draining the breast—can be performed safely during pregnancy. In a study of premenopausal non-pregnant patients who underwent peritumoral injection of 12 MBq of technetium-99m (99m-Tc), the radioactive tracer was found only at the injection site and in the sentinel node, with none traceable in the abdomen. This confirmed that the tracer does not reach the fetus in measurable amounts.

Safety was also confirmed in another study involving 25 pregnant patients who underwent the procedure using 99m-Tc and/or methylene blue dye. However, if a sentinel lymph node procedure is performed, blue dye (Patent Blue®) should be avoided, as it carries a small risk of a severe allergic reaction (anaphylaxis) in the mother, which could subsequently cause fetal distress.

Clinical Implications: What This Means for Patients

For women diagnosed with breast cancer during pregnancy, these findings translate into several practical and important messages:

• You can be treated during pregnancy. Modern cancer treatment, including surgery and chemotherapy after the first trimester, is safe for both mother and baby when performed at a specialized center.
• Delaying treatment is rarely the right choice. Termination of pregnancy has not been shown to improve outcomes, and delaying cancer treatment to avoid treatment during pregnancy can worsen the mother's prognosis while also increasing the risks of prematurity from early delivery.
• Being diagnosed during pregnancy does not automatically mean your tumor is different. While PrBC is statistically more likely to be triple-negative or higher grade, the overall approach is to treat it according to standard guidelines based on your specific tumor's biology.
• Specialized multidisciplinary care matters. Treatment decisions involve balancing complex oncological, obstetrical, and fetal considerations, so having a team experienced in cancer in pregnancy is essential.
• Some treatments are off-limits during pregnancy. Endocrine therapy and HER2-targeted therapy (such as trastuzumab) are contraindicated while pregnant, and these treatments are typically deferred until after delivery.
• Fetal monitoring is standard. Growth ultrasounds and monitoring during surgery help ensure the baby is developing well and identify any complications early.
• Long-term follow-up of children is recommended. Children exposed to cancer treatment in the womb should be followed in dedicated centers to track their development over time.

Limitations of This Research

While this review provides a comprehensive summary of current evidence, several limitations should be acknowledged. First, much of the data on breast cancer during pregnancy comes from observational cohort studies rather than randomized controlled trials, which are difficult to conduct in pregnant patients for ethical and practical reasons. Second, the relatively small number of patients in some studies limits the statistical power and generalizability of findings. Third, the research on long-term outcomes for children exposed to cancer treatment during pregnancy is still evolving, with many questions remaining about subtle developmental effects that may only appear later in life. Fourth, the molecular and genetic findings, while promising, come from small studies and have not yet been fully validated in larger, prospective cohorts. Finally, the authors note that the incidence of breast cancer during pregnancy is rising due to delayed childbearing, meaning that ongoing research is needed to keep pace with changing demographics.

Recommendations for Patients

1. Report any breast changes promptly. If you notice a lump, nipple discharge, or other breast change that persists for 2 weeks or more during pregnancy, ask your doctor for a clinical breast examination and appropriate imaging (typically ultrasound). Do not assume it is just a normal pregnancy change.
2. Seek care at a specialized, multidisciplinary center. Look for a hospital or cancer center with experience treating cancer during pregnancy, including expertise in obstetrics, oncology, surgery, radiology, and pediatrics. Dedicated tumor boards for cancer in pregnancy can provide individualized recommendations.
3. Ask about genetic counseling. Because breast cancer at a young age can be associated with inherited mutations such as BRCA1 and CHEK2, genetic counseling and testing should be part of your care.
4. Discuss the full range of treatment options with your care team, including the timing of surgery

   Frequently Asked Questions

   Is it safe to receive breast cancer treatment while I am pregnant?

   Yes, in many cases. The research shows that surgery can be done in any trimester, and chemotherapy can be safely given after the 12th week of pregnancy. However, some treatments like endocrine therapy and HER2-targeted therapy are not used during pregnancy. A specialized multidisciplinary team should plan your treatment carefully.

   Will cancer treatment harm my baby?

   When treatment is planned by a specialized team, most women can continue their pregnancy. Chemotherapy after the first trimester is generally safe, but it has been linked in one large study to a higher chance of the baby being small for gestational age or needing neonatal intensive care. Fetal growth is monitored regularly during cancer treatment.

   Should I consider terminating my pregnancy to improve my cancer outcome?

   No. Termination of pregnancy has not been shown to improve maternal outcomes for breast cancer. Delaying cancer treatment or delivering early to start treatment after birth can be harmful. Starting cancer treatment during pregnancy may actually reduce the risks of prematurity by allowing the pregnancy to continue closer to full term.

   Is breast cancer during pregnancy more aggressive or different from other breast cancer?

   Compared to non-pregnant younger patients, pregnant patients in two large registries were more likely to have higher-grade tumors, hormone receptor-negative tumors, and triple-negative breast cancer. But the approach is to treat according to your specific tumor's biology using standard guidelines, just as for non-pregnant patients.

   What tests can I safely have to diagnose and stage breast cancer during pregnancy?

   Breast ultrasound is the first imaging choice and is completely safe. Mammography can also be used with abdominal shielding not being necessary. Contrast-enhanced MRI is generally avoided unless it will change your care. For staging, ultrasound and MRI are strongly preferred over CT or PET/CT scans, which are used only if necessary.

   Can I have breast surgery or a sentinel lymph node biopsy while pregnant?

   Yes. Breast cancer surgery can be performed safely during any trimester. Care is taken to position you appropriately after 20 weeks and to prevent problems like low blood pressure or low oxygen. Sentinel lymph node biopsy with a radioactive tracer is safe, but blue dye should be avoided due to a small risk of allergic reaction.

   What is the chance that my baby will be born alive and healthy after cancer treatment during pregnancy?

   In a large international study of 1,170 patients, 88% of singleton pregnancies resulted in a live birth, though 48% were preterm. Preterm births and NICU admissions were more common with chemotherapy exposure before birth. Careful monitoring and specialized care are essential to help protect the baby.

   Should I get a second opinion if my doctor recommends delaying breast cancer treatment until after I give birth?

   Yes, a second opinion is reasonable when treatment timing is uncertain. Breast cancer during pregnancy can often be treated safely with surgery and chemotherapy after the first trimester. Starting treatment during pregnancy rather than delaying delivery can lower prematurity risks, while postponing care may worsen the mother's prognosis. A multidisciplinary specialist team should guide decisions, and a second opinion can confirm whether your proposed plan follows standard pregnancy-specific protocols. Diagnostic Detectives Network provides independent expert second opinions.