RESUMO
BACKGROUND Venous thromboembolism (VTE), comprising deep vein thrombosis (DVT) and pulmonary embolism (PE), is a common, serious cardiovascular event. Predisposing factors include genetic disorders, immobility, and underlying malignancy. Soft tissue tumors are by contrast rare, but should be included in the differential etiology of DVT, especially when the patient is young and has few thrombotic risk factors. CASE REPORT We present a 40-year-old patient whose initial diagnosis was spontaneous DVT of the lower leg, treated conventionally. Subsequently, he developed progressive calf swelling, which was diagnosed as multifocal desmoid fibromatosis, a rare and complex soft tissue tumor. CONCLUSIONS DVT is common but soft tissue tumors are rare. The disparity in incidence of these very distinct pathologies may contribute to late diagnosis of occult soft tissue pathology. We discuss the incidence, etiology, pathology, diagnosis, and best management of both desmoid fibromatosis and DVT, which may co-exist in a causative way.