Pulmonary tumour thrombotic microangiopathy mimicking immunotherapy-associated pneumonitis.

We present a case of pulmonary tumour thrombotic microangiopathy (PTTM) in a patient on adjuvant immunotherapy for resected triple negative breast cancer. The patient presented with deranged liver function tests and subsequently developed severe hypoxia and thrombocytopaenia, with right heart failure. The primary differential diagnosis considered was immunotherapy-associated hepatitis and pneumonitis. Despite organ support, the patient deteriorated rapidly and died of respiratory failure. As is often the case with PTTM, the diagnosis was only found at postmortem. PTTM should be considered in patients with a background of cancer (and may be more common in certain subtypes) who present with this unusual combination of clinical features. While the condition carries an extremely poor prognosis, prompter recognition for future patients may allow consideration of novel treatments.