Phase 1 study of dabrafenib in pediatric patients (pts) with relapsed or refractory BRAF V600E high- and low-grade gliomas (HGG, LGG), Langerhans cell histiocytosis (LCH), and other solid tumors (OST).

Abstract Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasia with a highly variable clinical presentation affecting people of all ages. Mutations in BRAF V600E are the most identifiable molecular alteration in LCH although its incidence in pediatric patients with isolated pituitary stalk involvement is not well described. Pediatric patients with LCH and isolated pituitary stalk involvement typically present with central diabetes insipidus. Diagnosis requires a transcranial biopsy which often yields scant tissue. We sought to determine the prevalence of BRAF V600E mutations in patients with isolated pituitary stalk LCH using digital droplet polymerase chain reaction because this method requires minimal tumor DNA. We identified 8 patients with isolated pituitary stalk thickening who underwent a biopsy at Children’s Hospital Colorado from January 2001 to December 2019, as well as 6 patients with systemic LCH diagnosed by biopsy in the same period as a comparison. Only one out of the 8 patients with isolated thickened pituitary stalk was found to have a detectable BRAF V600E mutation. Five out of the 6 patients with systemic LCH had a detectable BRAF V600E mutation. In our series, BRAF V600E mutations are rare in pediatric patients with LCH and isolated pituitary stalk involvement.

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

Journal of Clinical Oncology ◽

10.1200/jco.2020.38.15_suppl.10524 ◽

2020 ◽

Vol 38 (15_suppl) ◽

pp. 10524-10524

Author(s):

Kelly C. Goldsmith ◽

Arnauld Verschuur ◽

Daniel A. Morgenstern ◽

Natasha van Eijkelenburg ◽

Sara Michele Federico ◽

...

Keyword(s):

Solid Tumors ◽

Pediatric Patients ◽

Wilms Tumor ◽

Phase 1 ◽

B Cell Lymphoma ◽

Complete Response ◽

Low Grade ◽

Open Label ◽

Therapy Regimen ◽

Best Response

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.

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