HER2-positive breast cancer diagnosed during pregnancy and later spread to bone and brain

What happened, in summary

A 38-year-old woman who was 21 weeks pregnant found a large mass in her right breast. Examination showed a 9 × 11 cm breast tumour with mobile axillary lymph nodes. Biopsy confirmed grade 2 invasive ductal carcinoma with ER 0%, PR below 1%, HER2 3+, and a Ki-67 of 10%–20%. An axillary-node biopsy also contained metastatic adenocarcinoma. Pregnancy-adjusted staging did not initially show distant disease. Because the cancer was locally advanced, she received four cycles of doxorubicin and cyclophosphamide every 3 weeks from weeks 22 to 31 of gestation. Reduced fetal movement prompted caesarean delivery at week 34, and she delivered a healthy boy. Postpartum imaging then identified an L3 bone lesion concerning for metastasis, confirmed on spinal MRI, and a possible sacral lesion. She began weekly paclitaxel with trastuzumab and pertuzumab. BRCA testing found a variant of uncertain significance in BRCA2. After counselling, she chose bilateral mastectomy, including prophylactic removal of the left breast. Residual cancer was ER 90%, PR below 1%, and HER2 3%; sentinel nodes were negative. She completed postmastectomy radiation and continued HER2-directed therapy because of residual and metastatic disease. Surveillance PET scans showed no new lesions. About 14 months after completing paclitaxel and radiation, she developed persistent headaches and nausea. Imaging revealed a right occipital brain lesion with oedema, herniation, and midline shift. Despite steroids and intensive care, she rapidly became unresponsive and died.