(P 261) CLINICAL FEATURES AND TREATMENT OUTCOMES OF PATIENTS WITH DESMOID TUMORS: A LARGE SINGLE INSTITUTION RETROSPECTIVE SERIES

Objective: Desmoid tumors are benign neoplasms comprised of monoclonal fibroblasts. While they are not reported to metastasize, they can be locally aggressive, leading to significant morbidity. Resection was previously the mainstay of treatment but given the possibility of prolonged stable disease, the paradigm has shifted to more watchful waiting or systemic therapies. Medical treatments, however, are not benign and with new therapies on the horizon it is best to understand the current state of desmoid treatment outcomes to optimize care.

Methods: The soft tissue sarcoma database at Levine Cancer Institute was queried to identify all patients treated for desmoid tumor from January 2008-January 2022. Demographics, clinical features, treatment regimens and surgical details were collected. For patients who underwent resection, recurrence free survival (RFS) was measured from resection date. RFS was evaluated by Kaplan-Meier methodology, with log rank tests utilized to compare RFS between cohorts.

Results: A total of 96 patients treated for desmoid tumor were identified; 78 patients had sufficient data available for inclusion. Median age at diagnosis was 37.5 years (range 1-80 years), 62% were female (84% premenopausal), 63% white and 32% black. Antecedent surgery at the desmoid location occurred in 30% of patients (4% with prior trauma). Twenty-seven percent of patients were diagnosed with another neoplastic process unrelated to FAP.

Surgical treatment was the initial treatment choice in 63% of patients. Ninety percent of new cases were resected from 2007-2011, 66% from 2012-2016 and 19% from 2017-2021. The 1-year and 5-year RFS were 89.4% and 69.3%, respectively. Oncologic surgeons performed 69% of the resections versus 31% performed by non-oncologic surgeons. RFS was longer among patients who had resection by an oncologic surgeon with 5-year RFS of 77.4% versus 5-year RFS of 48.5% for non-oncologic surgeon (p=0.093). Tumor extended to ≤ 1mm of resection margins (considered positive margin) in 84% of cases. Five-year RFS was not significantly different between margin status groups (69.8% for positive vs 71.4% for negative; p=0.815).

Among the patients who did not have upfront resection, 55% had first-line treatment with NSAIDs, 24% with sorafenib, 7% with methotrexate and vinca alkaloid, 7% with external beam radiation therapy, 3.5% with dacarbazine and doxorubicin, and 3.5% with observation alone. First-line systemic treatment led to stable disease in 31%, decreased tumor size in 25%, progressive disease in 24%, with 7% discontinuation due to toxicity, 7% unknown, and 3.5% discontinuation due to patient choice.

Conclusion: This relatively large single-institution retrospective analysis of desmoid tumors reflects prior reports that this tumor often occurs in younger patients with predisposing factors including hormone production and prior surgery. Surgical resection led to prolonged RFS and while margin status did not seem to impact RFS, the surgeon-type favored resection performed by oncologic surgeon. Intriguingly, non-FAP related neoplasms were commonly noted among patients with desmoid tumors, prompting the need for further investigation.