Pregnancy and Breast Cancer
Background
Breast cancer complicates roughly 1 in 3,000 pregnancies and is the most common cancer diagnosed in pregnancy. Pregnancy-associated breast cancer occurs in a younger population and is more often high-grade or oestrogen-receptor-negative, but pregnancy itself does not worsen prognosis once matched for age and stage. Care must be multidisciplinary, with the obstetric team as core members alongside breast surgeons, oncologists and breast care nurses.
Diagnosis in Pregnancy
- Any woman presenting with a breast lump in pregnancy should be referred promptly to a breast specialist team; diagnosis can be delayed because physiological breast changes mask lumps.
- Ultrasound is the first-line imaging test. If cancer is confirmed, mammography (with fetal/abdominal shielding) is used to assess extent of disease and the contralateral breast.
- Tissue diagnosis is by ultrasound-guided core biopsy for histology, not cytology — proliferative pregnancy change makes cytology unreliable.
- Staging for metastases is only performed with high clinical suspicion, using chest X-ray and liver ultrasound; bone scanning and CT (including pelvic CT) are avoided because of fetal irradiation. Gadolinium-enhanced MRI is reserved for specific clinical problems only, given limited safety data. Tumour markers (CA15-3, CEA, CA125) are unreliable in pregnancy and not recommended.
Treatment Timing and Safety by Trimester
- Surgery (breast-conserving surgery or mastectomy, with axillary staging) can be performed safely in any trimester. Sentinel node biopsy using radioisotope is acceptable (negligible uterine radiation), but blue dye is avoided as fetal effects are unknown.
- Chemotherapy is contraindicated in the first trimester because of a high rate of fetal abnormality. From the second trimester onward, standard anthracycline-based regimens are considered safe; there are fewer safety data for taxanes, which are generally reserved for high-risk or metastatic disease. Chemotherapy should stop at least 2–3 weeks before planned delivery to allow maternal bone marrow recovery and reduce neutropenia risk at birth.
- Radiotherapy is contraindicated during pregnancy (except for life- or organ-saving indications, e.g. spinal cord compression) and is deferred until after delivery.
- Endocrine and targeted therapy: tamoxifen and trastuzumab (Herceptin) are contraindicated throughout pregnancy — trastuzumab is associated with oligohydramnios/anhydramnios and tamoxifen with fetal teratogenicity — and should be deferred to the postpartum period.
- Timing of delivery is individualised; most women reach term with normal or induced delivery. If corticosteroids are needed for fetal lung maturation ahead of early delivery, this is discussed with the multidisciplinary team.
Breastfeeding Advice
- Women should not breastfeed while receiving chemotherapy, as cytotoxic drugs cross into breast milk and can cause neonatal leucopenia and infection risk. If breastfeeding is desired after chemotherapy ends, an interval of at least 14 days from the last chemotherapy dose is recommended to allow drug clearance; breastfeeding must stop again if chemotherapy is restarted.
- Tamoxifen and trastuzumab: breastfeeding should not occur while taking either drug, as transfer into breast milk is not established as safe.
- After completion of treatment, women can be reassured they may breastfeed from the unaffected breast; there is no evidence this increases recurrence risk. Radiotherapy to the treated breast typically causes fibrosis that makes lactation from that breast unlikely, but breast-conserving surgery alone may not prevent it.
High-Yield Exam Points
- Ultrasound first, then mammography with shielding; core biopsy (not cytology) for histology.
- Bone scan, CT and pelvic X-ray avoided in pregnancy; chest X-ray + liver ultrasound used for staging if indicated.
- Chemotherapy: contraindicated 1st trimester; anthracyclines safe from 2nd trimester; stop ≥2–3 weeks before delivery.
- Tamoxifen and trastuzumab are contraindicated in pregnancy and while breastfeeding (Grade D recommendation).
- No breastfeeding during chemotherapy; resume only after a ≥14-day drug-clearance interval from the last dose.
- Radiotherapy deferred until after delivery unless life- or organ-saving.
Source: RCOG Green-top Guideline No. 12 (Third edition, last reviewed 26 August 2025 (published in *BJOG* Nov 2025, Vol 132(12):e194–e228; next review 2028). Full third-edition text is paywalled on Wiley; the clinical detail below is verified against the RCOG-published second edition (March 2011), whose core diagnostic and treatment positions remain the standard teaching for MRCOG.)
Read the original on rcog.org.uk
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