Paraneoplastic acquired haemophilia A in extensive-stage small cell lung cancer (ES-SCLC) in the era of immunotherapy.

Small cell lung cancer (SCLC) is a deadly and rapidly progressive disease that can present with various paraneoplastic syndromes on initial workup. Acquired factor VIII (FVIII) deficiency, also known as acquired haemophilia A (AHA), has been identified as a rare paraneoplastic syndrome in SCLC. Here, we present a 61-year-old woman with a massive gastrointestinal bleed and prolonged activated partial thromboplastin time (PTT) in the emergency department. She was diagnosed with rare paraneoplastic AHA secondary to extensive-stage SCLC (ES-SCLC). She was treated with high-dose steroids and factor bypassing agents, which led to the resolution of bleeding and undetectable FVIII inhibitor levels. She was subsequently treated for ES-SCLC with carboplatin, etoposide and atezolizumab. This case report highlights a rare clinical presentation of paraneoplastic AHA that necessitates prompt recognition in patients with SCLC with ongoing bleeding and elevated PTT.