Breast Cancer in Pregnancy

Definition

• During pregnancy
• In the first postpartum year
• At any time during lactation

Epidemiology

• Breast cancer is the most common non-gynecologic malignancy associated with pregnancy
• ~1 in 1,000 pregnancies complicated by breast cancer in the US; ~10,000 cases/year worldwide
• Incidence: 17.5–39.9 per 100,000 births (postpartum rates higher than during pregnancy itself)
• 10–20% of breast cancers in women in their 30s are discovered during pregnancy
• Incidence is increasing due to delayed childbearing and younger age of breast cancer diagnoses
• Women with first pregnancy after age 35 have an increased risk of breast cancer; those before age 20 have a 50% reduced risk

Pathology / Histology

• Invasive ductal carcinoma (NOS) accounts for 78–88% of cases
• Triple-negative phenotype is disproportionately common, accounting for ~50–60% of PABC
• Higher histologic grade, larger tumor size, more frequent lymph node involvement, and lower ER/PR expression compared to non-pregnant patients
• ER negativity is likely due to downregulation of estrogen receptors during the hyperestrogenic state of pregnancy
• Higher proportion of inflammatory breast cancer

Clinical Presentation & Diagnosis

Presentation

• Most common: painless palpable breast mass
• Milk rejection sign — infant refuses to nurse from one breast; may indicate an occult carcinoma
• Diagnostic delays of ≥2 months are common due to physiologic engorgement and increased nodularity
• A 1-month delay in treatment increases risk of axillary metastasis by 0.9–1.8%
• Any discrete lump present for 2–4 weeks should be biopsied

Differential Diagnosis of a Breast Mass in Pregnancy

Imaging

Biopsy

• Core-needle biopsy is preferred — safe, reliable, performed under local anesthesia
• Fine-needle aspiration is an alternative but requires experienced pathologist (pregnancy-related proliferative changes can cause false indeterminate results)
• Risk of milk fistula ~1.4%; reduced by emptying breast before procedure; breastfeeding cessation is not mandatory if fistula develops
• Always send for ER, PR, HER2 immunohistochemistry

Staging

• AJCC TNM staging is used, same as non-pregnant patients
• PABC typically presents at a later stage than non-pregnant women (attributed to diagnostic delay, not the biology of pregnancy per se)
• Axillary staging:
  • Palpable nodes → ultrasound-guided FNA
  • Sentinel lymph node biopsy (SLNB) with technetium-99m sulfur colloid is safe in all trimesters (fetal dose <20 μGy)
  • Blue dyes (isosulfan blue, methylene blue) are contraindicated — risk of anaphylaxis and fetal methemoglobinemia

Management

Multidisciplinary Team

Termination of pregnancy does not improve maternal prognosis. Treatment should adhere as closely as possible to non-pregnant standards.

Surgery

• Avoid maternal hypoxia and hypotension; maintain MAP ≥60 mmHg for uterine perfusion
• After 20 weeks: left lateral tilt to displace uterus off IVC
• After 24 weeks: intraoperative fetal monitoring required

• First trimester: Mastectomy is standard (BCS is not appropriate because radiation cannot follow immediately)
• Second trimester: Mastectomy or BCS; BCS must be followed by adjuvant chemo during remainder of pregnancy, then radiation postpartum
• Third trimester: Both mastectomy and BCS acceptable; postpartum radiation follows
• Immediate tissue expander reconstruction is safe and feasible in all trimesters

Chemotherapy

Contraindicated Treatments During Pregnancy

Endocrine Therapy

• Hormone receptor-positive tumors: tamoxifen deferred until after delivery
• Oncotype Dx 21-gene assay may still provide useful prognostic information in selected patients

Delivery & Monitoring

• Delivery planned 3–4 weeks after last chemotherapy cycle
• Timing based on maternal condition, treatment needs, and neonatal outcome expectations
• Women with PABC have a significantly higher rate of preterm delivery (61.2% vs. 8% in general population)
• Breastfeeding is contraindicated during chemotherapy or radiotherapy; lactation from a treated breast is not otherwise contraindicated

Prognosis

• When matched for stage and tumor characteristics, survival outcomes are similar to non-pregnant women
• The apparently worse prognosis historically reported reflects later stage at diagnosis, not pregnancy itself
• A 2.8-fold increase in metastasis and 2.7-fold increase in mortality has been observed in patients ≤40 years diagnosed within 5 years postpartum

Pregnancy After Breast Cancer

• Three large registry studies show no poorer prognosis in women who become pregnant after successful treatment
• Oncologists generally recommend delaying pregnancy 2–3 years after initial treatment (most recurrences occur within the first 2 years)
• Some reports even suggest an antitumor effect of subsequent pregnancy

Key Takeaways

1. Any breast lump in pregnancy must be evaluated — ultrasound first, then core biopsy if solid
2. Termination does not improve prognosis; standard treatment should proceed
3. Surgery is safe in all trimesters; safest in the 2nd trimester
4. Chemotherapy safe after week 14; stop ≥3 weeks before delivery
5. Radiation, trastuzumab, tamoxifen, and methotrexate are contraindicated during pregnancy
6. Blue dye for SLNB is contraindicated; use technetium-99m only
7. Multidisciplinary management is essential
8. Congenital abnormality rate in chemo-exposed infants (~3%) is comparable to the general population

Chemotherapy in Breast Cancer in Pregnancy

General Principles

Timing by Trimester

First Trimester (Weeks 1–12) — CONTRAINDICATED

• Spontaneous abortion
• Congenital malformations
• Fetal death

Second & Third Trimester (from Week 14 onward) — SAFE

Stop Before Delivery

• Allow recovery from myelosuppression (neonatal pancytopenia, neutropenia, risk of sepsis at delivery)
• Prevent drug accumulation in the fetus
• Reduce risk of bleeding or infection in mother at delivery

The placenta should be sent for pathologic evaluation — placental metastasis has been reported, though fetal metastasis has not.

Pharmacokinetics in Pregnancy

Recommended Regimens

Safe Agents (2nd and 3rd Trimester)

Standard Regimens Used

• AC — Doxorubicin + Cyclophosphamide
• FAC/FEC — 5-Fluorouracil + Doxorubicin/Epirubicin + Cyclophosphamide (the only prospective study of chemo in PABC used FAC in 24 patients — no birth defects, median delivery at 38 weeks)
• AC + Taxane — Doxorubicin + Cyclophosphamide followed by Paclitaxel or Docetaxel

Some investigators advocate weekly epirubicin (shorter nadir periods reduce risk if unexpected delivery occurs), but this is not standard — maternal prognosis should not be compromised to limit unproven fetal damage.

Dose-Dense Regimens

Agents Contraindicated During Pregnancy

For HER2-positive disease: chemotherapy (anthracycline/taxane backbone) proceeds during pregnancy; trastuzumab is deferred until after delivery.

Neoadjuvant vs. Adjuvant Setting

• Chemotherapy may be given in either adjuvant or neoadjuvant settings during pregnancy
• If neoadjuvant: start at week 14, continue standard cycles as tolerated; surgical decision (mastectomy vs. BCS) follows postpartum if needed
• Neoadjuvant approach is particularly useful for locally advanced disease — allows definitive surgery to be deferred while systemic therapy proceeds during pregnancy

Supportive Care During Chemotherapy

Fetal & Neonatal Outcomes

• Congenital malformation rate ~3% — comparable to the national average for the general population
• ~50% of infants exposed to chemo in 2nd/3rd trimester show fetal growth restriction, prematurity, or low birth weight — normalizes over time
• No long-term cognitive or developmental deficits have been demonstrated
• Preterm delivery rate is significantly elevated (61.2% vs. 8% in the general population)
• Taxane systematic review (PMID 38166767, 2024): Among 159 patients (55% breast cancer, mostly paclitaxel), obstetric and fetal outcomes were generally similar to the general obstetric population when taxanes were used after the first trimester — live birth in all cases with known outcome; preterm delivery in 54.5%; SGA in 30.3%; 7 congenital malformations (5.3%)

Breastfeeding

Key Points Summary