Mutational Testing in Gastrointestinal Stromal Tumor

Drugs in the GIST Field (Therapeutic Targets and Clinical Trial Staging)

BACKGROUND

Molecular targeted therapies are the most important type of medical treatment for GIST, but the development of GIST drugs and their targets have not been summarized.

METHODS

Drugs in the field of GIST were analyzed and collated through Pharmaprojects, ClinicalTrials. gov and PharmaGO databases.

RESULTS

As of 2021, there are 75 drugs that have appeared in the GIST clinical trials. The six most frequent targets in GIST clinical trials, in descending order of frequency, were KIT, PDGFRA, KDR (VEGFR2), FLT3, FLT1 (VEGFR1), and FLT4/VEGFR3. Only 8 drugs are in preclinical research. There are challenges in the development of new drugs for GIST.

CONCLUSION

This article analyzes and summarizes the general situation of GIST drugs, the target distribution of GIST drugs, and the trends in GIST drug-related clinical trials.

Utilization of Mutational Analysis (MA) in Gastrointestinal Stromal Tumor (GIST) Management in British Columbia (BC) Between January 2008 to December 2017: a Retrospective Population-Based Study

PURPOSE

To examine oncologists' practice pattern of ordering MA in localized and metastatic GISTs in British Columbia (BC).

METHODS

Patients diagnosed with GIST from January 2008 to December 2017 in BC were identified. Chart review was performed to determine clinical characteristics and the use of MA as part of their oncologic care.

RESULTS

The cohort included 411 patients: median age 64 (18-94 years), 49.1% male, primary site included stomach (53%), small intestine (32%), and others (15%). Sixty-nine percent had localized disease, while 13% presented with de novo metastatic disease and 18% had recurrent metastatic disease. MA was ordered in 41% of the patients overall, 28% in localized, and 70% in metastatic settings (63% in de novo metastasis and 78% in recurrent metastasis). Among patients with localized disease, higher MA use rates were observed among those undergoing neoadjuvant/adjuvant treatment (45%) compared to those not receiving systemic therapy (18%). While MA use rates in localized GIST did not change over time (28.5% before 2015 and 28% after 2015), MA use in metastatic disease increased from 54% before 2015 to 79% after 2015. Among all MA ordered for metastatic disease, 82.4% were ordered at the time of de novo metastatic diagnosis, and 77.4% were ordered either at the time of recurrent metastatic diagnosis or earlier when the disease was localized.

CONCLUSION

MA use has remained stable for localized disease but has increased after 2015 in the metastatic setting which may be due to evolving sequencing technology, expansion of metastatic treatment options, and enhanced awareness of MA.

Optimal Avapritinib Treatment Strategies for Patients with Metastatic or Unresectable Gastrointestinal Stromal Tumors

BACKGROUND

Avapritinib, a novel inhibitor of KIT/PDGFRA, is approved in the U.S. for the treatment of adults with PDGFRA exon 18-mutant unresectable or metastatic gastrointestinal stromal tumors (U/M GISTs). We assessed the safety of avapritinib and provide evidence-based guidance on management of avapritinib-associated adverse events (AEs), including cognitive effects and intracranial bleeding.

MATERIALS AND METHODS

We performed a post hoc analysis of data from a two-part, single-arm dose escalation/expansion phase I study (NAVIGATOR; NCT02508532) in patients with U/M GISTs treated with oral avapritinib 30-600 mg once daily. The primary endpoints were safety and tolerability; the impact of dose modification (interruption and/or reduction) on progression-free survival (PFS) was a secondary endpoint. Efficacy analyses were limited to patients who started avapritinib at 300 mg (approved dose).

RESULTS

Of 250 patients enrolled in the study, 74.0% presented with KIT mutation and 24.8% presented with PDGFRA exon 18-mutation; 66.8% started avapritinib at 300 mg. The most common treatment-related AEs (any grade) were nausea (59.2%), fatigue (50.0%), periorbital edema (42.0%), anemia (39.2%), diarrhea (36.0%), vomiting (36.0%), and increased lacrimation (30.8%). No treatment-related deaths occurred. Among 167 patients starting on 300 mg avapritinib, all-cause cognitive effects rate (grade 1-2) was 37.0% in all patients and 52.0% in patients ≥65 years. Cognitive effects improved to a lower grade more quickly with dose modification (1.3-3.1 weeks) than without (4.9-7.6 weeks). Median PFS was 11.4 months with dose modification and 7.2 months without.

CONCLUSION

Tolerability-guided dose modification of avapritinib is an effective strategy for managing AEs in patients with GISTs.

IMPLICATIONS FOR PRACTICE

Early recognition of adverse events and tailored dose modification appear to be effective approaches for managing treatment-related adverse events and maintaining patients on avapritinib. Dose reduction does not appear to result in reduced efficacy. Patients' cognitive function should be assessed at baseline and monitored carefully throughout treatment with avapritinib for the onset of cognitive adverse events. Dose interruption is recommended at the first sign of any cognitive effect, including grade 1 events.

Financial Implications of Avapritinib for Treatment of Unresectable Gastrointestinal Stromal Tumors in Patients With a PDGFRA Exon 18 Variant or After 3 Previous Therapies in a Hypothetical US Health Plan

IMPORTANCE

With the approval of avapritinib for adults with unresectable or metastatic gastrointestinal stromal tumors (GISTs) harboring a platelet-derived growth factor receptor alpha (PDGFRA) exon 18 variant, including PDGFRA D842V variants, and National Comprehensive Cancer Network guideline recommendations as an option for patients with GIST after third-line treatment, it is important to estimate the potential financial implications of avapritinib on a payer's budget.

OBJECTIVE

To estimate the budget impact associated with the introduction of avapritinib to a formulary for metastatic or unresectable GISTs in patients with a PDGFRA exon 18 variant or after 3 or more previous treatments from the perspective of a US health plan.

DESIGN, SETTING, AND PARTICIPANTS

For this economic evaluation, a 3-year budget impact model was developed in March 2020, incorporating costs for drug acquisition, testing, monitoring, adverse events, and postprogression treatment. The model assumed that avapritinib introduction would be associated with increased PDGFRA testing rates from the current 49% to 69%. The health plan population was assumed to be mixed 69% commercial, 22% Medicare, and 9% Medicaid. Base case assumptions included a GIST incidence rate of 9.6 diagnoses per million people, a metastatic PDGFRA exon 18 mutation rate of 1.9%, and progression rate from first-line to fourth-line treatment of 17%.

EXPOSURES

The model compared scenarios with and without avapritinib in a formulary.

MAIN OUTCOMES AND MEASURES

Annual, total, and per member per month (PMPM) budget impact.

RESULTS

In a hypothetical 1-million member plan, fewer than 0.1 new patients with a PDGFRA exon 18 variant per year and 1.2 patients receiving fourth-line therapy per year were eligible for treatment. With avapritinib available, the total increase in costs in year 3 for all eligible adult patients with a PDGFRA exon 18 variant was $46 875, or $0.004 PMPM. For patients undergoing fourth-line treatment, the total increase in costs in year 3 was $69 182, or $0.006 PMPM. The combined total budget impact in year 3 was $115 604, or $0.010 PMPM, including an offset of $3607 in postprogression costs avoided or delayed. The higher rates of molecular testing resulted in a minimal incremental testing cost of $453 in year 3.

CONCLUSIONS AND RELEVANCE

These results suggest that adoption of avapritinib as a treatment option would have a minimal budget impact to a hypothetical US health plan. This would be primarily attributable to the small eligible patient population and cost offsets from reduced or delayed postprogression costs.