4526 - Long-term outcome of neoadjuvant tyrosine kinase inhibitors (TKI) in locally advanced dermatofibrosarcoma protuberans (DFSP)

Background

Imatinib mesylate is approved in unresectable tumors and has been also proposed in the neoadjuvant setting in order to reduce tumor size and post-operative relapses for difficult to resect DFSP. The aim of this study was to evaluate the long-term results of neoadjuvant imatinib and other TKI used in DFSP.

Methods

The files of all patients with the following criteria seen from 2007 to 2017 in our center were collected in this retrospective study: a/histologically proven primary or recurrent DFSP with COL1A1-PDGFB translocation b/ difficult to treat but surgically manageable as assessed in pluridisciplinary tumor board, c/received first-line neoadjuvant TKI (imatinib, pazopanib). The primary endpoint was long-term progression-free survival (PFS).

Results

27 patients (median 42 years, range: 18-63) were included, of whom 9 (33%) had fibrosarcomatous transformation on pre-TKI biopsy. 10 patients had primary tumors and 17 presented recurrences. Median tumor size was 6 cm (range 3-30). 24 patients received imatinib (median dose= 600mg/day), 3 received pazopanib (median dose= 600mg/day) for a median of 7 months. The best MRI response to ITK treatment before surgery according to RECIST1.1 consisted of complete/partial response (33%) or stability (48%). DFSP was surgically removed in 24 patients (89%) after a median of 7 months and 2 surgeries. Two patients (7%) did not receive surgery because of metastasis progression. One other patient declined surgery. 23 of 24 patients surgically treated were disease-free after 50 months of median follow-up (range 10-133). One patient developed distant metastasis 37 months after the complete surgical resection. The median PFS was 44 months (range 10-133).The histological response localization was mainly patchy (n = 10) or diffuse (n = 7). The median percentage of therapeutic response surface was 65%.Treatment-related adverse events occurred in 23 patients (85%). 4 patients had grade 3 or higher toxicities (2 grade 3 and 4 neutropenia, 1 grade 3 cholestasis, 1 grade 3 nausea) requiring temporary treatment disruption and dose reductions.

Conclusions

TKI are effective neoadjuvant treatment for locally advanced or inoperable DFSP with long-term PFS and few severe adverse events.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.