Durable partial response with low-dose, intermittent nivolumab in combination with gemcitabine for high PD-L1 metastatic triple-negative breast cancer: a case report.

Immune checkpoint inhibitors (ICIs) have improved outcomes in selected patients with metastatic triple-negative breast cancer (mTNBC), particularly those with high programed death-ligand 1 (PD-L1) expression. However, optimal dosing strategies balancing efficacy, toxicity, and cost remain unclear. We report the case of a 34-year-old woman with recurrent mTNBC and high PD-L1 expression (combined positive score, CPS ≥ 60; immunohistochemistry 22C3 pharmDx assay). She achieved durable disease control over 22 months (September 2024 to June 2026) using a combination of gemcitabine maintenance chemotherapy and low-dose intermittent nivolumab (40 mg fixed dose, administered 3-weekly). This de-escalated regimen was adopted due to early treatment toxicity and severe financial constraints. The patient achieved a confirmed partial response by RECIST v1.1 criteria (48% reduction in target lesion size), accompanied by manageable CTCAE Grade 2 hypothyroidism requiring oral levothyroxine replacement. This case illustrates that in biomarker-selected, PD-L1-high mTNBC, combination chemotherapy with low-intensity PD-1 blockade can maintain prolonged antitumor activity. These observations support the working hypothesis of a minimum effective immune dose, warranting prospective evaluation in resource-constrained clinical settings.