The first report of pediatric patients with solid tumors treated with venetoclax

10524 Background: Dependence on the prosurvival protein B-cell lymphoma 2 (BCL-2) occurs in certain pediatric solid tumors, resulting in tumorigenesis and resistance to therapies. Venetoclax (VEN), an orally administered BCL-2-selective inhibitor, has preclinical anticancer activity in human-derived neuroblastoma models. Reported here are preliminary results from pediatric patients (pts) with recurrent or refractory (R/R) solid tumors treated with VEN monotherapy or VEN with cyclophosphamide and topotecan (Cy-Topo). Methods: This phase 1 open-label, 2-part study (NCT03236857) enrolled pts < 25 yr old with R/R malignancies; we report only on pts with solid tumors. Following a dose ramp-up, pts received 800 mg VEN (age/weight-adjusted adult equivalent) once daily for the first 8 wk; Cy-Topo was added optionally after wk 8. Dose-limiting toxicities (DLTs) were assessed during the first 21 days of VEN therapy or cycle 1 of VEN-Cy-Topo. Objectives included safety, toxicity, and preliminary efficacy. Results: As of Dec 17, 2019, 11 solid tumor pts were enrolled: neuroblastoma (n = 6), rhabdomyosarcoma (n = 2), Wilms’ tumor, Carney-Stratakis syndrome, and low-grade fibromyxoid sarcoma (n = 1 each). Median age was 11 yr (range 3–22); median time on study was 6.9 mo (range 1.2–17.8). All pts experienced ≥1 treatment-emergent adverse event (TEAE); vomiting (72%; all grades) was most common. Grade ≥3 TEAEs were reported in 82% of pts; febrile neutropenia (64%), decreased blood cell count, and neutropenia (36% each) were the most common. Seven pts received 800-mg monotherapy for 8 wk; 3 of these pts did not receive Cy-Topo after monotherapy. Of the 7 pts who received VEN-Cy-Topo, 3 pts received 400 mg VEN with Cy-Topo. DLTs of grade 4 neutropenia/thrombocytopenia with delayed count recovery occurred in 2 pts on 800 mg VEN-Cy-Topo, necessitating a dose de-escalation (to 400 mg VEN). Grade 4 neutropenia occurred in 2 pts on 400 mg VEN with Cy-Topo, leading to the addition of myeloid growth factor to the therapy regimen. The best response after 8 wk of VEN monotherapy was stable disease (SD). Six pts were evaluable for tumor response with VEN-Cy-Topo; 1 neuroblastoma pt had a complete response after 5 cycles of 400 mg VEN, 4 pts had SD (3 on 800 mg and 1 on 400 mg VEN) and 1 (800 mg VEN) had progressive disease as best response. Conclusions: Continuous dosing of VEN with Cy-Topo was not tolerated due to cytopenias in 4/7 pts with solid tumors. Discontinuous dosing of VEN with Cy-Topo is being explored. Clinical trial information: NCT03236857.