(P 401) LONG-TERM OUTCOMES OF IMATINIB-TREATED DERMATOFIBROSARCOMA PROTUBERANS: INSIGHTS FROM A SINGLE-INSTITUTION CASE SERIES

Objective: Dermatofibrosarcoma protuberans (DFSP) is a rare, monoclonal cutaneous soft tissue sarcoma with an indolent growth pattern and an incidence of 4.1 cases per million. It is characterized by a fusion of COL1A1 and PDGFB, rendering the tumor susceptible to PDGFR inhibition with imatinib. Imatinib has demonstrated efficacy in both metastatic and localized disease, including DFSP with fibrosarcomatous transformation (DFSP-FS). It is often used neoadjuvantly to reduce tumor size, enabling resection with minimal cosmetic or functional compromise. Some patients remain disease-free following resection and discontinuation of therapy; however, resistance and adverse effects can limit long-term efficacy.

Methods: We present a case series illustrating the natural history of DFSP treated with imatinib, highlighting both the successes and challenges of therapy in real-world clinical settings outside of trial protocols.

Results: • Case 1: A patient with large, localized DFSP was started on neoadjuvant imatinib. The tumor has shown continuous reduction in size, with surgical resection planned once stability is achieved.
• Case 2: A patient’s treatment was complicated by prolonged non-adherence to imatinib. Despite reinitiation, the tumor progressed locally, necessitating resection. The surgery resulted in significant postoperative morbidity.
• Case 3: A patient with DFSP-FS experienced prolonged remission on imatinib. After discontinuation due to adverse effects, she developed multiple distant recurrences, all resectable. Over 20 years post-diagnosis, her disease became clinically resistant to imatinib and is now managed as a high-grade sarcoma.

Conclusion: Imatinib remains a valuable therapeutic option for both metastatic and locally advanced DFSP, offering the potential for durable disease control and facilitating surgical resection in select cases. However, these cases highlight critical real-world challenges, including treatment-limiting side effects, the consequences of non-adherence, and the emergence of resistance over time. Long-term management requires a multidisciplinary approach, patient education, and close monitoring to optimize outcomes. These findings underscore the need for prospective studies and real-world data registries to better define optimal treatment duration, identify predictors of response, and guide management of resistance in DFSP.