What happened, in summary

A 63-year-old woman was diagnosed with Stage II triple-negative invasive ductal carcinoma of the left breast. A germline PALB2 variation was also reported. She began pembrolizumab with paclitaxel and carboplatin. After her third cycle, she developed rapidly worsening numbness and weakness in both legs, along with bowel and bladder problems.

Testing supported an inflammatory myelitis related to pembrolizumab rather than metastatic cancer. Her cancer treatment was held, and she received high-dose steroids and plasma exchange followed by a prolonged steroid taper. At discharge she could not walk and needed a wheelchair, but neurologic recovery continued over time. Five months later she could walk with a walker, and by 2 years she could walk short distances without assistance.

The breast cancer responded strongly to the initial systemic treatment. CT and breast ultrasound showed a complete radiographic response. Six months after the hospitalization, she underwent left partial mastectomy. No residual cancer was found in the breast, and all 3 sentinel lymph nodes were negative. She later completed adjuvant radiation. Her breast cancer showed a strong response, while recovery from the severe immune-related neurologic complication required prolonged treatment and rehabilitation.