Inflammatory breast cancer is a rare and aggressive form of breast cancer. Venous thromboembolism is often related to cancer conditions but this report presents a case in which the thromboembolic event predicted the diagnosis of cancer. A 48-year-old female was admitted with the evidence of acute right axillary vein thrombosis. There was also erythema and edema of the skin of the right breast. Further evidence revealed a case of inflammatory breast cancer. The patient underwent anticoagulant therapy, and neoadjuvant systemic chemotherapy was initiated. The patient underwent extensive unilateral mastectomy following neoadjuvant chemotherapy. Follow-up (after 2 months of anticoagulation therapy for deep vein thrombosis) revealed recanalization of the right axillary vein, without evidence of residual thrombus. A case of acute vein thrombosis as the first manifestation of breast cancer may delay the diagnosis and subsequent appropriate treatment.