Abstract
Background: Immune checkpoints are molecules that serve to augment or inhibit the immune response. The treatment landscape for numerous tumors now relies significantly on immune checkpoint inhibitors (ICIs). Pembrolizumab, a subset of ICIs specifically focused on the programmed cell death 1 (PD-1) molecule. By blocking PD-1, these inhibitors enhance the ability of the immune system to fight cancer cells. Although PD-1 inhibitors are critical in cancer treatment, their use can be associated with immune-related adverse events, such as ICI-related sarcoid-like reaction. Case Presentation: This report describes a 49-year-old female patient with stage IIIA breast cancer breast cancer who developed ICI-related sarcoid-like reaction after starting a neoadjuvant chemoimmunotherapy regimen that included Pembrolizumab. After 4 months of ongoing treatment, she started having significant nausea and vomiting. Computed tomography (CT) scans performed during hospitalization revealed multiple pathologically enlarged thoracic lymph nodes, suspicious for disease progression. Initially, the laboratory workup and cultures were unrevealing. However, esophagogastroduodenoscopy and bronchoscopy were performed, showing noncaseating granulomas in both the stomach and thoracic lymph node biopsy samples. The patient was diagnosed with a sarcoidosis-like reaction to Pembrolizumab. Notably, her symptoms rapidly improved upon initiating systemic corticosteroids. Follow-up CT scan showed a significant improvement in lymphadenopathy after discontinuing Pembrolizumab. Conclusion: This case emphasizes the significance of acknowledging sarcoid-like reactions as possible adverse effects of Pembrolizumab. Given the rising utilization of PD-1 inhibitors, it becomes imperative to be mindful of such adverse events. This awareness helps avoid misdiagnosing disease progression and aids in making informed decisions about ongoing treatment with ICIs.