Abstract One cause of constitutional syndrome in patients previously submitted to valve replacement surgery is a prosthetic endocarditis; this occurs in 1-6% of valve surgeries and has an adverse prognosis. Although this is a likely etiology, it is important to keep other possibilities in mind. This clinical case is about a 61 years old male, with known history of smoking, atrial fibrillation anticoagulated with warfarin (with low TTR), and rheumatic fever in childhood, with severe aortic stenosis/regurgitation and moderate mitral regurgitation. In August 2018 he was admitted in our hospital with mitral valve endocarditis cause by Streptococcus agalactiae. He was submitted to an aortic and mitral valve replacement surgery with 2 bioprothesis. Three months later he was admitted again with weight loss, fatigue, dyspnea for small efforts and worsening anemia. The first diagnosis hypothesis was prosthetic endocarditis. The echocardiogram showed normo-functioning aortic bioprothesis; obstructive mitral bioprothesis with an image suggestive of a vegetation; and a de novo mass in the left auricle, compatible with a thrombus. This clinical case was discussed in Heart Team: as the patient was clinically stable, it was opted for an initial conservative approach; although there was a strong clinical suspicion that all the clinical case was due to thrombotic manifestations (assuming that the vegetations had a non-infectious origin), he was nonetheless medicated with vancomycin, gentamicin and rifampicin, as the diagnosis of early culture negative prosthetic endocarditis could not be discarded. He was anticoagulated with enoxaparin. In the reevaluation echocardiogram there was a significative reduction of the left atrial thrombus and disappearance of the mitral valve vegetation image, with improvement of the mitral valve prosthetic gradients. The case was discussed again in Heart Team: due to the clinical evolution, the hypothesis that this was all caused by a thrombotic manifestation grew stronger; it was opted not to submit the patient to a new surgery and the antibiotic therapy was suspended. To study the pro-thrombotic state and the constitutional syndrome, a full body CT was requested: "hilar-mediastinal and bilateral hilar adenopathy; right supraclavicular adenopathy; splenomegaly with infarcted area." The right hilar adenopathy was biopsied; the pathologic exam revealed non-small cells lung carcinoma. The patient was discharged, medicated with warfarin and oriented to outpatient Oncology consult. Any cancer can be associated with thrombotic manifestations. In this case, considering the heavy smoking burden, lung cancer is one of the first etiologies to consider. The thrombotic manifestations of the non-small cells lung carcinoma are due to a paraneoplastic mechanism and might precede the cancer diagnosis. This clinical case highlights the importance of thinking of different etiologies in the differential diagnosis of a constitutional syndrome. Abstract P1310 Figure. Left auricle mass