Pazopanib therapy for desmoid tumors in adolescent and young adult patients.

BACKGROUND: Desmoid tumors/aggressive fibromatosis (DT/AF) lack a reliably effective medical therapy. Surgical resection may be morbid and does not preclude recurrence. Radiation may carry severe late effects, particularly detrimental in young patients. At our institution, we recently observed promising results with pazopanib therapy for DT/AF in adolescent and young adult (AYA) patients.

PROCEDURE: Retrospective single-institution chart review.

RESULTS: Six DT/AF patients of 3-21 years with previously treated DT/AF received pazopanib; 31 DT/AF patients received established therapies only. In both groups, median age at diagnosis was 16 years, female patients comprised 50%, and most common DT/AF site was extremity. Established therapies showed few objective responses and most patients therefore received multiple therapies. Surgical resection had a 68% recurrence rate. Of eight patients who received vinblastine/methotrexate, only one had a partial response (PR) by RECIST 1.1 and five had stable disease (SD); 62.5% required additional therapy. Of seven patients who received sulindac/tamoxifen, none showed objective improvement. In contrast, pazopanib demonstrated best responses by RECIST of PR in two of seven and SD in six of seven tumors. A PR of 66% was observed in a patient who had failed multiple prior therapies. The mesenteric DT/AF also showed PR. Maximum volumetric decrease by T2-weighted magnetic resonance imaging (MRI) was 97%. Dramatically increased fibrosis was seen on T2-weighted MRI. Patients reported pain relief and improvement in function within 1 month. Except for one case of edema, all other toxicities responded to dose reduction without sacrificing objective treatment response.

CONCLUSION: Pazopanib provides a promising, well-tolerated therapy for DT/AF in the AYA population and warrants further study.