Description
The therascreen PIK3CA RGQ PCR Kit is a real-time qualitative in vitro diagnostic PCR test for the detection of 11 mutations in the phosphatidylinositol 3-kinase catalytic subunit alpha (PIK3CA) gene using a sample of DNA extracted from either formalin-fixed, paraffin-embedded (FFPE) breast tumor tissue or K 2 EDTA anticoagulated blood plasma, taken from a patient with breast cancer. The therascreen PIK3CA RGQ PCR Kit is the first companion diagnostic (CDx) test approved by the FDA to aid in the selection of patients with breast cancer who may be eligible for treatment with the alpha-selective PI3K-inhibitor, PIQRAY (alpelisib), in combination with the estrogen receptor antagonist, fulvestrant.
The SOLAR-1 study (CBYL719C2301) was a randomized, double-blinded, placebo-controlled, international, multicenter Phase III clinical trial that compared treatment with PIQRAY plus fulvestrant with placebo plus fulvestrant in men and postmenopausal women with hormone receptor-positive, HER2-negative advanced breast cancer that had progressed on or after aromatase inhibitor treatment. A total of 572 breast cancer patients were enrolled into two cohorts, with or without a PIK3CA mutation. Patients were randomized to receive PIQRAY 300 mg plus fulvestrant or placebo plus fulvestrant in a 1:1 ratio. The primary endpoint was progression-free survival (PFS) determined using RECIST v1.1 criteria, based on investigator assessment. Results using FFPE tissue specimens SOLAR-1 showed that in patients whose tumors harbored specific PIK3CA mutations, treatment with PIQRAY plus fulvestrant prolonged median PFS by a clinically meaningful 5.3 months (11 months overall) compared with treatment with placebo plus fulvestrant, and conferred an estimated 35% risk reduction in disease progression or death. Analysis of the CDx PIK3CA mutant-positive patient subset (347 patients) demonstrated that those receiving PIQRAY plus fulvestrant had an estimated 36% lower risk of disease progression or death (HR = 0.64; 95% CI: 0.48, 0.85) than patients receiving placebo plus fulvestrant. By contrast, PFS was also estimated in the therascreen PIK3CA RGQ PCR Kit-negative population and no PFS benefit was observed in those patients (HR = 0.85; 95% CI: 0.58, 1.25). The importance of establishing PIK3CA mutation status when identifying patients for treatment with PIQRAY plus fulvestrant is therefore clear; only patients whose tumors harbor actionable PIK3CA mutations are likely to experience a clinically meaningful increase in PFS. Results using plasma specimens K 2 EDTA anticoagulated peripheral venous whole blood clinical plasma specimens collected from breast cancer patients randomized in SOLAR-1 prior to initiation of study treatment (baseline) were tested retrospectively with the therascreen PIK3CA RGQ PCR Kit to evaluate concordance between tissue and plasma results. Of the 328 therascreen PIK3CA RGQ PCR Kit tissue-positive patients, 179 were therascreen PIK3CA RGQ PCR Kit plasma-positive. Of the 215 therascreen PIK3CA RGQ PCR Kit tissue-negative patients, 209 were therascreen PIK3CA RGQ PCR Kit plasma-negative. There were no invalid plasma results (Table 1). Table 1. Correspondence table between therascreen PIK3CA RGQ PCR Kit tissue results and therascreen PIK3CA RGQ PCR Kit plasma results therascreen PIK3CA RGQ PCR Kit - tissue Positive Negative Invalid Total therascreen PIK3CA RGQ PCR Kit - plasma Positive 179 6 1 186 Negative 149 209 5 363 Invalid 0 0 0 0 Total 328 215 6 549 Agreement (PPA, NPA and OPA) between the therascreen PIK3CA RGQ PCR Kit plasma and therascreen PIK3CA RGQ PCR Kit tissue results was calculated using the therascreen PIK3CA RGQ PCR Kit tissue results as reference (Table 2). The point estimates of PPA, NPA and OPA were 55%, 97% and 72%, respectively. Table 2. Agreement between therascreen PIK3CA RGQ PCR Kit plasma results and therascreen PIK3CA RGQ PCR Kit tissue results using the therascreen PIK3CA RGQ PCR Kit tissue results as reference Measure of agreement Percent agreement % (N) Two-sided 95% CI Positive percent agreement (PPA) 55% (179/328) 49.0%, 60.1% Negative percent agreement (NPA)* 97% (209/215) 94.0%, 99.0% Overall percent agreement (OPA) 72% (388/543) 67.5%, 75.2% * 95% CI calculated using the Clopper-Pearson Exact method. The therascreen PIK3CA RGQ PCR Kit therefore enables reliable selection of breast cancer patients with PIK3CA alterations who may be eligible for treatment with PIQRAY.
The therascreen PIK3CA RGQ PCR Kit is comprised of six reaction mixes; one control reaction targeting exon 15 and five mutation-specific reactions utilized to detect 11 mutations in exons 7, 9 and 20 of the PIK3CA gene (Exon 7: C420R; Exon 9: E542K; E545A, E545D [1635G>T only], E545G, E545K, Q546E, Q546R; and Exon 20: H1047L, H1047R, H1047Y). Allele-specific technology allows accurate and highly reproducible detection of mutations; DNA is selectively amplified using ARMS primers, probes and PCR clamps, with sensitive signal detection using the Rotor-Gene Q MDx (US) instrument. Result reporting is fully automated. If both the run controls and the sample results are valid, the therascreen PIK3CA RGQ PCR Kit qualitatively determines the mutation status of the DNA samples and reports if the sample contains a mutation(s).
The simple and straightforward testing workflow begins with manual DNA extraction from either FFPE breast tumor tissue (using the QIAamp DSP DNA FFPE Tissue Kit) or from K 2 EDTA anticoagulated plasma (using the QIAamp DSP Circulating Nucleic Acid Kit), followed by sensitive real-time PCR on the Rotor-Gene Q MDx (US) instrument. Rotor-Gene AssayManager software rapidly and accurately determines mutations and reports results, informing the system operator if one or more of the 11 mutations detected by the kit are present. The kit is a qualitative assay that can yield results in less than two working days.
