Neoadjuvant denosumab treatment of locally advanced giant cell tumor of bone (GCTB).
11026 Background: Retrospective study on locally advanced GCTB patients (pts) treated with neoadjuvant Denosumab (Db) outside clinical trials in 6 European reference centers. Methods: From 138 pts (median age 30yrs) with histologically confirmed advanced GCTB treated with Db(2011-2016), we included into analysis 87pts who underwent surgery after preoperative Db. All 87 patients had locally advanced tumors with extensive soft tissue involvement(54) or penetration to joint, not amenable to limb-sparing surgery/primary curettage or with high risk of recurrence. In 39/42(93%) cases diagnosis was confirmed by H3F3Agene mutation. Median follow-up time -22 months. Results: Primary tumor was located in lower limb(54%; n = 47) -mostly in tibia(25%) and femur(23%), upper limb(33%; n = 29), and pelvis/axial skeleton/ribs(13%; n = 11). 68(78%) patients had primary tumors, 19(22%) recurrent tumors after surgery (+/-radiotherapy). Median Db duration was 7months (range 1.5-35months), 17pts received also Db postoperatively. 39(45%) had wide en-bloc resection -WE (+17 implantation of prosthesis), 48(55%) cases had intralesional curettage -C, no extremity amputation. Pts who underwent prosthetic replacement had longer median preoperative Db therapy as compared to pts without prosthesis. All pts demonstrated a response to Db Progression after surgical treatment was observed in 15 pts -13 of them after intralesional curettage (13/48, 27%); 9 patients underwent D re-challenge -all responded. Two-year progression-free survival (PFS; from Db start) rate was 80%, 91% in WE group vs 73% in C group (p = 0.04), one-year PFS (from operation date) rate was 84%: 92% in WE and 79% in C group(p = 0.01). Treatment was well tolerated with only 1 grade 3 toxicity. Conclusions: Our study confirms that Db is active in a neoadjuvant setting with excellent efficacy and short-term tolerability. It implies that neoadjuvant therapy with Db is the option for treatment of initially locally advanced tumors to facilitate complete surgical resection or avoid mutilating surgery. The risk of recurrences after curettage of GCTB following Db raises questions about the optimal duration of preoperative treatment and if Db is indicated postoperatively.