Triple-negative breast cancer: partial response to immunotherapy combination

What happened, in summary

This patient was 41 when she was diagnosed in July 2017 with Stage IIA pT1cN1 breast cancer. Immunohistochemistry showed triple-negative disease: ER-negative, PR-negative, HER2-negative, with Ki-67-positive cells above 80%. She underwent left mastectomy and axillary lymph-node dissection in August 2017, followed by 4 cycles of doxorubicin, 12 cycles of paclitaxel, and radiotherapy. She then continued regular follow-up. In February 2023, when she was 47, PET imaging raised concern for recurrence. Further evaluation supported metastatic spread to the left lung and neck and mediastinal lymph nodes, and she received a clinical diagnosis of Stage IV rT0N3M1 recurrent breast cancer. Pembrolizumab plus MK-4830 began in March 2023. After 9 months of immunotherapy, serial CT scans showed a partial response: tumor burden had decreased, lung and mediastinal metastases were smaller, and no new metastatic lesions had appeared. At the same time, she developed a grade 2 drug-induced lichen-planus-like eruption, with confluent flat-topped red papules on the arms and legs, especially the backs of the hands and feet. The plaques were thick, violaceous, hyperkeratotic, and had Wickham striae. Skin biopsy from the back of the hand confirmed lichenoid eruption. High-potency topical corticosteroids were not enough, so prednisone 40 mg daily was given for 2 weeks, then tapered to 5 mg maintenance. The rash improved enough for pembrolizumab and MK-4830 to continue without dose reduction or discontinuation. At 2-month follow-up, the skin symptoms had not recurred. Mucosal, scalp, and nail examinations were unremarkable, and routine blood, biochemical, coagulation, and infection testing did not show another explanation for the eruption.