Lung cancer (LC) is linked to an increased risk of cancer-associated thrombosis (L-CAT), requiring anticoagulant therapy (AT). Patients treated with AT have an increased risk of bleeding. Hemoptysis is common and potentially severe in LC patients. The risk of hemoptysis in l -CAT patients who initiated AT remains unknown.

A retrospective observational study was conducted in patients with l -CAT who initiated AT, from January 1, 2010, to December 31, 2022. The primary aim was to determine the incidence of hemoptysis within 6 months of follow-up. Secondary aims were to assess risk factors for hemoptysis, its clinical impact, and its association with 6-month mortality.

Among 108 L-CAT patients, 9 developed a hemoptysis at 6 months (8.33%, 95% CI [3.12–13.54]). Main risk factors identified were history of bleeding (OR 16.88, 95% CI [3.68–77.30]), tumor size >7 cm (OR 5.29, 95% CI [1.34–20.85]), squamous cell carcinoma (OR 4.48 [1.15–17.42), endobronchial bud at endoscopy (OR 10.81 [2.05–74.18]). The median time to hemoptysis onset was 9 days. Events were of low abundance, recurrent and non-fatal. Two patients required hospital admission, one of whom needed aerosol vasopressin therapy. Relative risk of death at 6 months was 1.29, (CI 95% [0.80–2.07]) in patients with hemoptysis, compared to those without.

Nearly one in ten patients with l -CAT experienced hemoptysis, typically within the first days of treatment. Though generally non-severe and not directly fatal, these events highlight the need for close monitoring. Further research is needed to clarify the impact on prognosis.