Infantile myofibromatosis (IM) is a disorder characterized by proliferation of benign myofibroblastic tumors that typically manifest as solitary or multiple nodules in the skin, muscle, bone, subcutaneous tissues, and visceral organs and can pose significant morbidity and mortality risks, particularly in cases involving visceral organs or causing functional impairment. These soft tissue lesions present before age two and can undergo spontaneous regression or are amenable to surgical resection. Successful clinical management with low dose metronomic chemotherapy (Methotrexate and Vinblastine) is possible and can treat extensive disease as seen in our patient.

Background: Children with cancer diagnosis are overall at a higher risk of thrombosis. For a newly diagnosed bland thrombus, patients are commonly started on anticoagulants to prevent further extension and embolization of the clot. In the rare instance that a pediatric patient has a tumor thrombus, the role of anticoagulation is less clear. Procedure/Methods: Patients under 21 years of age with a finding of tumor thrombus on imaging from 2010-2020 at Texas Children’s Hospital were identified and their medical records were reviewed. Results: A total of 50 patients were identified. Most thrombi were incidental findings at diagnosis; however, there were two patients who presented with pulmonary embolism (PE). Inferior Vena Cava extension was noted in 36% of the patients and 24% patients had an intracardiac tumor thrombus. Hepatoblastoma (26%) was the most common malignancy associated with tumor thrombus. Anticoagulation was initiated in 10 patients (20%). Only 2 of these 10 patients showed response to anticoagulation. However, 40% (4/10) patients in the anticoagulation cohort were noted to have bleeding complications (p <.05). Conclusion: Children with intravascular extension of solid tumors were not commonly started on anticoagulation at the time of diagnosis, irrespective of the extent of tumor thrombus. Furthermore, we observed a significant trend toward higher incidence of bleeding complications after initiation of anticoagulation. There is inadequate evidence at this time to support routine initiation of anticoagulation in pediatric patients with intravascular extension of solid tumors.