Long-Term Survival Following Nivolumab Treatment in Pulmonary Tumour Thrombotic Microangiopathy Associated With Cancer of Unknown Primary: A Case Report.

Pulmonary tumour thrombotic microangiopathy (PTTM) is a rare but frequently fatal condition characterized by rapidly progressive pulmonary hypertension and right heart failure caused by tumour microemboli in the pulmonary vasculature. We report the case of a 64-year-old man who presented with rapidly progressive respiratory failure. Chest computed tomography demonstrated centrilobular nodules and a tree-in-bud (TIB) pattern. Pulmonary perfusion scintigraphy and transthoracic echocardiography suggested pulmonary hypertension with multiple peripheral perfusion defects, raising strong clinical suspicion for PTTM. Transbronchial lung biopsy (TBLB) revealed TTF-1-positive adenocarcinoma, although the primary tumour site remained undetermined. Based on these findings, clinically suspected PTTM was diagnosed and nivolumab monotherapy was promptly initiated as systemic treatment for the underlying malignancy. Despite transient severe deterioration, the patient's respiratory function improved markedly, and he has remained progression-free for more than 3 years. This case highlights the importance of early clinical recognition of PTTM and prompt initiation of appropriate systemic therapy, even before definitive identification of the primary tumour when clinically warranted.