Surgical Experience from the Phase III STASEY Trial of Emicizumab Prophylaxis in Persons with Hemophilia A with FVIII Inhibitors: Final Analysis

Background: Emicizumab, a bispecific monoclonal antibody, bridges activated factor (F) IX and FX, replacing the function of missing activated FVIII in persons with hemophilia A (PwHA). The Phase IIIb, multicenter, single-arm STASEY study (NCT03191799) assessed the safety and efficacy of emicizumab prophylaxis in PwHA with FVIII inhibitors. Surgical experiences in STASEY are reported here.

Methods: Following informed consent and ethics committee approval, PwHA aged ≥12 years with FVIII inhibitors received 3 mg/kg/week emicizumab for 4 weeks (loading dose), then 1.5 mg/kg/week for the remaining 2-year treatment period. Minor and major surgeries were managed per the investigators' discretion. The type and number of procedures performed, additional prophylaxis, and frequency and management of postoperative bleeds were analyzed. Surgeries occurring up to 28 days after the last dose of emicizumab were included, due to emicizumab's ~28-day half-life (Emicizumab Prescribing Information, United States Food and Drug Administration, 2017). Surgeries were documented using an electronic case report form by the treating physicians and classified as minor or major based on manual medical review (Santagostino, et al. Haemophilia, 2015). Bleed and prophylactic hemophilia medication data were recorded in the electronic Bleed Medication Questionnaire by participants. Case narratives were provided by trial investigators.

Results: Overall, 46 patients reported ≥1 on-study surgery. Thirty-seven patients had 56 minor surgeries (central venous access device [CVAD], n=9; dental, n=20; joint, n=4; other, n=23) (Figure), one of which (skin laceration and suture insertion on Day 9) was performed during the loading phase. Twenty-four surgeries (42.9%) were managed with additional prophylactic medications (Table). Of these, 11/24 (45.8%) resulted in postoperative bleeds, of which 6/11 were treated (54.5%). Of surgeries managed without additional prophylactic medications, 15/32 (46.9%) resulted in postoperative bleeds, of which 5/15 (33.3%) were treated.

A total of 13 patients had 22 major on-study surgeries (arthroplasty, n=13; other, n=9). 'Other' included hemorrhoid operations, coronarography, sigmoidectomy, colostomy, laparotomy and polypectomy. Eighteen (81.8%) major surgeries, including all arthroplasties, were managed with additional prophylactic medications (Table). Of these, 12/18 (66.7%) resulted in postoperative bleeds (including 10/13 arthroplasties), of which six (50.0%) were treated (all arthroplasties). Four (18.2%) major surgeries were managed without additional prophylactic medication, including three hemorrhoid operations in one patient, and a coronarography in a patient with acute myocardial infarction. One hemorrhoid operation resulted in a postoperative treated bleed.

Major surgeries included a 55-year-old male with Grade 4 device dislocation of left knee prosthesis on Day 7, who was diagnosed with recurrent infection and prosthesis misalignment on Day 62. Amputation of the left leg above the knee was performed, with treatment including tranexamic acid and rFVIIa. A 61-year-old male with left knee prosthesis infection underwent left knee arthrodesis on Day 457, vacuum-assisted closure therapy on Day 495, skin grafting on Day 512, and left knee arthrodesis with skin flap placement on Day 527. Throughout these surgeries, the individual experienced recurrent joint bleeding and received rFVIIa. Neither of these individuals had a change in their study treatment due to these events.

No thrombotic events (TEs) or thrombotic microangiopathies (TMAs) related to surgeries were observed.

Conclusions: In the STASEY study of PwHA with FVIII inhibitors receiving emicizumab prophylaxis, most minor surgical procedures were performed without additional prophylactic coagulation factor and did not result in postoperative treated bleeds. Therefore, emicizumab alone provided adequate hemostatic coverage for some PwHA undergoing certain types of minor surgery, such as tooth extraction and CVAD removal. Major surgeries were safely performed with additional coagulation prophylaxis. Management of surgeries with rFVIIa did not result in TE or TMA. In case of bleeds, a bleed management plan should be in place. Effects of emicizumab on coagulation and assays may persist for up to 6 months after the last dose, which may be relevant when planning postoperative treatment.

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