The therascreen PDGFRA RGQ PCR kit has become the first FDA-approved companion diagnostic designed to detect platelet-derived growth factor receptor alpha gene mutations.
The FDA has approved the therascreen platelet-derived growth factor receptor alpha (PDGFRA) RGQ PCR kit (therascreen PDGFRA kit) as a companion diagnostic for identifying patients with gastrointestinal stromal tumors (GIST) who may benefit from treatment with tyrosine kinase inhibitor (TKI) avapritinib (Ayvakit), according to a press release from QIAGEN, N.V.1
The therascreen PDGFRA kit was designed to detect the D842V somatic variant in the PDGFRA gene. Moreover, avapritinib targets the PDGFRA exon 18 D842V mutation, which has demonstrated primary resistance to other TKIs when expressed in patients in patients with GIST. The test is the first FDA-approved PDGFRA assay available as a companion diagnostic.
The therascreen assay makes use of genomic DNA extracted from formalin-fixed paraffin-embedded (FFPE) tumor samples that are processed and prepared with the QIAamp DSP DNA FFPE Tissue Kit. The Rotor-Gene Q MDx instrument is also employed to amplify DNA and detect mutations.
“The therascreen PDGFRA kit is an FDA-approved and validated test, delivering results in a fast turnaround time,” Jonathan Arnold, vice president and head of Translational Science and Precision Diagnostics at QIAGEN, said in the press release. “This ensures that physicians receive results promptly, enabling them to make informed treatment decisions for their patients [with GIST] in a timely and effective manner.
The FDA approved avapritinib for unresectable or metastatic GIST harboring a PDGFRA exon 18 mutation in January 2020.2 Supporting efficacy data for this approval came from the phase 1 NAVIGATOR study (NCT02508532), in which investigators evaluated avapritinib in adult patients with unresectable GIST or other relapsed or refractory solid tumors.
According to findings published in European Journal of Cancer, treatment with avapritinib elicited an overall response rate (ORR) of 91% (n = 51/56) in patients with PDGFRA D842V-mutated GIST regardless of prior thereapy.3 Among those receiving the 300 mg or 400 mg starting doses, the ORR was 95% (n = 36/38), which included complete responses (CRs) in 13% and partial responses (PRs) in 82%. Additionally, the ORR in the TKI-naïve population was 91% (n = 10/11), which included CRs in 27% and PRs in 64%.
Among patients with PDGFRA D842V–mutated disease (n = 56) and those in the overall safety population (n = 250), respectively, the most common adverse effects included nausea (68% and 64%), diarrhea (66% and 45%), anemia (66% and 54%), and fatigue (63% and 63%).
“Today's approval of [avapritinib] brings forward a new standard of care for patients with PDGFRA exon 18 mutant GIST, a genomically defined population that previously had very limited treatment options,” study investigator Michael Henrich, MD, professor of Medicine at Oregon Health & Science University, said in a press release at the time of the FDA’s approval of avapritinib.2
Investigators of the open-label, non-randomized phase 1 NAVIGATOR study assessed avapritinib in patents with unresectable or metastatic GIST at 17 treatment sites across 9 countries. In part 2, the dose expansion portion of the trial, patients received a starting dose of avapritinib at 400 mg once a day, which investigators reduced to 300 mg once a day.
The study’s primary end points were ORR and safety. Secondary end points included clinical benefit rate, duration of response, and progression-free survival.