Immunotherapy directed at the programmed cell death-1 receptor (PD-1) or its ligand PD-L1 has proven effective in solid malignancies such as melanoma, non-small cell lung cancer (NSCLC), urothelial cancer, renal cell carcinoma, and head and neck cancer. Compared with cytotoxic chemotherapy, radiotherapy, or molecular targeted agents, immunotherapy is an innovative strategy for treating malignancies, with durable clinical responses and manageable adverse events. Thymic carcinomas are extremely rare, constituting only 0.06% of all malignancies, are much more aggressive tumours than thymomas and have a worse prognosis. Nowadays, first line platinum-based chemotherapy for metastatic tumours are the cornerstone of treatment. However, the results of further therapeutic lines for metastatic or relapsed thymic carcinoma are unsatisfactory, with no regimen showing a consistent benefit. Moreover, the rarity of these tumours makes it difficult to carry out clinical trials. Herein we report a remarkable result of 1 year stable disease with good quality of life and no side effects obtained from the use of immunotherapy with pembrolizumab in a case of heavily pre-treated squamous cell thymic carcinoma and cardiac impairment. We also include a literature review of clinical trials on PD-1/PD-L1 inhibitors for the treatment of thymic epithelial cancers, taking a close look at cardiac toxicity.