Background: Pulmonary Embolism (PE) is a life-threatening condition with annual incidence ranging from 39 to 115 cases per 100,000 population [1]. Along with many other causes, neoplasia is one of the highest risk factors for pancreatic, lung, gastric, cerebral and haematological cancer [2]. Patients with neoplasia often have venous thromboembolism (VTE) during the course of the disease, but occasionally neoplasia is diagnosed as secondary to VTE.

Case Presentation: A 55-year-old man known with high blood pressure and dyslipidaemia is diagnosed with bilateral distal Deep Venous Thrombosis (DVT) and treated with a factor Xa inhibitor. Two months later he is admitted for fatigue, dry cough, unwanted weight loss of approximately 5kg for a month and progressive exertion dyspnea. The echocardiographic examination reveals dilated right chambers with thrombus in the Right Ventricle (RV). The suspicion of pulmonary embolism it was confirmed on thoracic contrast CT examination. Large bilateral mediastinal adenopathies and a right lung nodule were also visualised on lung CT scan. The patient was treated with unfractionated heparin, slow-acting nitrate, aspirin, calcium blocker, with the disappearance of the thrombus from the right ventricle. Bronchoscopy showed a lesion near the right main bronchus. The diagnosis of pulmonary adenocarcinoma is confirmed histopathologically on the sample obtained at bronchoscopy and from the mediastinal lymph node obtained at mediastinoscopy. The patient was referred to the oncology service for specialised treatment.

Conclusion: VTE under anticoagulant treatment should always raise some suspicions and other causes should be sought. Undiagnosed neoplasms , drug resistance or drug interactions, thrombophilias are some of the causes that should be suspected in case of thrombosis under therapeutic anticoagulant.