CHICAGO – Loxo Oncology will seek US Food and Drug Administration approval for larotrectinib as a treatment for patients with TRK fusion-positive tumors after three-quarters of participants in a combined analysis responded to the drug.
The data presented at the American Society of Clinical Oncology, with additional follow up and blinded confirmation via central radiology review, will support a new drug application to the FDA for larotrectinib, Loxo Oncology CEO Joshua Bilenker said. If approved, larotrectinib will be another option for patients whose specific genomic characteristics will determine whether he or she receives the drug, regardless of where in their bodies the tumors occur.
At the meeting, David Hyman from Memorial Sloan Kettering Cancer Center discussed combined analysis from a Phase I, Phase I/II, and Phase II study involving a total of 55 adult and pediatric patients with TRK fusions across 17 unique cancer types, and showed that 76 percent responded to the therapy. In those studies 12 percent saw their tumors entirely disappear while 64 percent saw theirs tumors partially shrink.
Two patients with complete responses were able to have surgery that may be potentially curative, Hyman highlighted. More than 90 percent of responding patients remained on therapy as of the April 14 cutoff, and 91 percent of those who responded remained progression free after six months of treatment.
Of the 24 percent who didn't respond, half the patients had stable disease and the other half saw their disease progress. In the study, one breast cancer patient didn't respond to the drug, but Bilenker said that in other studies Loxo has observed breast cancer patients with TRK fusions respond to larotrectinib. Another patient with a rare type of appendix cancer also didn't respond to the drug. Based on this data, Bilenker is satisfied that the hypothesis to target TRK fusions holds up.
However, the patients that responded reported "dramatic improvement of their symptoms" within days of starting treatment with larotrectinib. The drug was well tolerated by patients, with 13 percent requiring dose modifications, and no patients discontinued from the trial due to toxicities.
"I believe these data demonstrate that larotrectinib is consistently and durably effective in TRK fusion-positive cancers regardless of tumor type," Hyman said at the meeting.
Loxo has been in discussions with the FDA about the larotrectinib program for the past year and a half, and expects to submit the NDA later this year or early next year, with the potential for an FDA decision by mid-2018. As the only selective pan-TRK inhibitor currently in clinical development, larotrectinib could "potentially be the first novel targeted therapy that's developed and eventually used in a tumor-agnostic manner," Hyman said.
TRK fusions occur in between 1,500 and 5,000 cancer patients per year, comprising 1 to 3 percent of cancer cases. "This study, due to the rarity of TRK fusions, required patients to travel from around the world," Hyman said. "It really was a heroic effort on the part of the patients, many of whom flew transcontinentally, monthly to be in this study."
Though in certain commonly occurring cancers TRK fusions occur infrequently, in some rare cancer types TRK fusions tend to be a defining feature. The 12 pediatric patients in this study tended to have infantile fibrosarcoma and other types of sarcomas and thyroid cancers, while the 43 adults had a variety of tumor types, including lung, breast, colon, pancreatic, melanoma, billiary, thyroid cancers, as well as sarcomas.
Patients were enrolled in the study based on results from 15 different lab tests, largely next-generation sequencing platforms. However, currently available diagnostics don't typically test for TRK fusions, and therefore acurate estimates of how many cancer cases may be characterized by this marker don't exist.
"Really recognizing this benefit in the community will require that we test patients more universally for the presence of TRK fusions or other tumor-agnostic biomarkers, such as micro-satellite instability," Hyman said. "To really enjoy these benefits, we'll have to change the paradigm in which we test these patients."
As the tissue-agnostic treatment paradigm catches on, comprehensive genomic profiling will need to be integrated more readily into patient care. The FDA recently approved Merck's Keytruda (pembrolizumab) in advanced cancer patients with microsatellite instability-high and mismatch repair deficiency regardless of tumor type.
As a result, there has been a "public validation" of the tissue-agnostic, biomarker-guided treatment approach, noted Bilenker. "It really tells the world that it's important to test all patients' actionable biomarkers," he said. "The more stories [of biomarker-guided treatments] that accumulate the more it improves this pitch to the lab medicine director who needs to think a little differently about the standard cancer workup."
However, there are cost considerations when broadly implementing any testing, particularly to identify rare genomic markers, such as TRK fusions. Studies conducted at academic and cancer centers looking at the clinical utility of precision oncology approaches using genomic profiling show that, on average, around 44 percent of patients have an actionable mutation, but around 11 percent receive a drug targeted at that marker.
As the number of actionable mutations increase, the cost-benefit implications of broad molecular profiling approaches will tip toward benefit, said Richard Carvajal, director of experimental therapeutics at New York-Presbyterian Columbia University Medical Center. "With large platform trials such as the NCI MATCH, it could be argued that routine broad molecular profiling should be performed for all patients with advanced malignancies," he said, but added that "the successful institution of such routine testing is very much dependent upon how the reimbursement patterns for these tests evolve."
Carvajal highlighted that one of the remarkable findings from the larotrectinib studies was the variety of testing assays used to gauge TRK fusions and that there was no apparent difference in outcomes based on the test used. "This mirrors other experiences, such as the identification of appropriate melanoma patients for BRAF based therapies where the sequencing platform utilized to identify BRAF mutations are comparable," he said.
For the time being, Loxo hasn't inked a formal companion diagnostic arrangement with an NGS test provider. The company earlier this year partnered with Roche subsidiary Ventana Medical Systems to develop an IHC test that can gauge TRK fusions in patients and identify best responders to larotrectinib. Loxo decided to advance an IHC companion test, according to Bilenker, because pathologists are familiar with the technology, it's economical to perform, and reimbursed more predictably compared to NGS testing.
"We want to see them all get better from a sensitivity standpoint in finding TRK fusions," Bilenker said of currently marketed NGS platforms. "We want to see them in the long run get reimbursed better. We want to see them all get adopted more often."
Although Hyman said that based on the data presented larotrectinib could become the new standard of care for cancer patients with TRK fusions, guidelines bodies would also need to weigh in as to when this treatment and testing should be offered to patients in their continuum of care.
Sumanta Pal from City of Hope agreed that just a few years ago this type of tissue-agnostic treatment paradigm was a pipe dream, but the larotrectinib development program brings cancer therapy into a new era where "treatment is truly based on mutation, and not location."
But the real challenge, he added, would be for oncologists to determine where larotrectinib would sit in treatment algorithms. "For rare cancers of course there is no established standard of care, such as salivary gland tumors, and there may be calls to screen for relevant mutations right away," he said. In the present analysis, 11 patients had salivary gland cancer.
"In the case of other diseases, such as colon cancer and prostate cancer, we'll really have to sit down and determine how larotrectinib sits against existing standards such as chemotherapy or hormone therapy," Pal said. "These elements will all play into at what juncture molecular testing is offered to determine candidacy for larotrectinib."
One of the disappointments of genomically-guided precision oncology treatments has been that after a period of response, the cancer always returns. Anticipating this, Loxo recently filed an investigational new drug application for a next-generation treatment, LOXO-195, for patients who become resistant to larotrectinib.
Hyman and colleagues published the pre-clinical rational for developing LOXO-195 in Cancer Discovery on June 3, and described how two patients who had become resistant to larotrectinib received the next-generation drug and had rapid tumor responses. "It's a pretty interesting thing to have the next-generation drug sitting in the ready even as the first drug isn't even approved yet," Bilenker said