What happened, in summary

A 33-year-old woman underwent breast-conserving surgery for right invasive breast carcinoma. Pathology showed a Stage II tumor with one involved axillary lymph node. The cancer was estrogen-receptor positive, progesterone-receptor positive, and HER2-positive.

Her postoperative treatment included chemotherapy and HER2-targeted therapy followed by radiotherapy. Soon after finishing radiotherapy, she developed a fever reaching 40°C and a severe headache. Blood tests showed neutropenia, while extensive testing did not identify a clear infectious organism. Brain MRI showed a small lesion in the splenium of the corpus callosum, consistent with reversible splenial lesion syndrome.

She received granulocyte-stimulating treatment, antibiotics, and medicines for fever and pain. Her fever and headache resolved, and repeat MRI showed that the brain lesion had disappeared. The reversible neurologic complication improved without a persistent abnormality on follow-up imaging.