Pericardial malignant infiltration as the cause of sudden death of a patient with metastatic urothelial carcinoma treated with atezolizumab

Background Muscle-infiltrating urothelial carcinoma of the bladder is the most common genitourinary cancer. Immunotherapeutic agents targeting protein-1 programmed death or protein-1 programmed death ligand are currently considered the standard treatment in patients with either inoperable locally advanced or metastatic urothelial carcinoma (MUC) after platinum-based chemotherapy failure. Case presentation Here we report the case of a Caucasian male patient with metastatic urothelial carcinoma treated with second-line atezolizumab within a trial who achieved complete response by computed tomography (CT), but suddenly died due to cardiac tamponade resulting from malignant pericardial infiltration. Histopathology confirmed this as the only site of disease progression. Conclusions Cardiovascular toxicity of atezolizumab was considered within differential diagnoses, however histopathological examination revealed progression of malignancy in the pericardium as the cause of the sudden death. This is the first published case report of a patient treated with second-line atezolizumab in whom the rare disease progression of pericardial infiltration was confirmed. Despite its rarity, the clinicians should always consider the possibility of pericardial metastases.