ATLANTA — GlaxoSmithKline last week released data from a phase III trial of its Tykerb breast cancer drug that it halted in April, and the results suggest that the drug is poised to become the next targeted therapy for that indication.
However, roles for Tykerb in other potential indications, such as renal cancer, seem less clear, according to phase II and III data presented here last week at the American Society of Clinical Oncology's 2006 meeting, held here this week.
The phase III trial studied Tykerb in combination with Roche's Xeloda in women with breast cancer who overexpressed Her2, and Glaxo halted the study in April after it reached its primary endpoint, time to disease progression.
Based on its findings from that study Glaxo will submit Tykerb for regulatory approval in the United States and Europe in the second half of the year, according to a company statement released this week. If approved, the drug will occupy the same market as Genentech and Roche's Herceptin, though not directly because Herceptin is approved as a monotherapy while Tykerb would be prescribed in combination with Xeloda.
"I do think the results show that the combination [of Tykerb and Xeloda] is an effective regimen" for women with this indication, said Charles Geyer of Allegheny Hospital during, who presented the phase III breast cancer data last week at ASCO.
"Even if [Tykerb] had a positive effect in this overexpressing group, it's probably not as good as these other agents."
In his presentation, Geyer said women with refractory advanced or metastatic Her2-positive breast cancer who failed Herceptin experienced an average time to progression of 36.9 weeks on Tykerb and Xeloda versus 19.7 weeks for women taking Xeloda alone. The trial included 392 patients who overexpressed Her2 by immunohistochemistry.
Renal Cell Carcinoma
Researchers last week also presented phase III data of Tykerb as a monotherapy in 417 patients with renal cancer. The researchers later reduced that population to a subgroup of 241 patients who overexpressed EGFR.
Alain Ravaud of the University Hospital of Bordeaux and University Victor Ségalen in Bordeaux, France, reported that Tykerb's effects on time to progression and survival were no different from hormone therapy among patients who had failed first-line cytokine therapy.
However, in the subgroup of 241 patients who overexpressed EGFR, those who took Tykerb experienced a greater median time to progression than patients on hormone therapy alone: 15.1 weeks versus 10.9 weeks, respectively. These results remained just outside of statistical significance though the overall survival of these patients was significantly longer with Tykerb — 46 weeks versus 37.9 weeks on hormone therapy.
The subgroup analysis looked at EGFR expression as measured by IHC, and a FISH analysis is ongoing.
But the subgroup analysis was post-hoc, Robert Figlin, a professor at the UCLA David Geffen School of Medicine and an audience member who sat in on the renal cell carcinoma presentation, told Pharmacogenomics Reporter this week. "The statistical design did not try to power the study in the proper way to address whether a subset would in fact have a positive result," he said. The study didn't have enough patients, and the two patient groups of EGFR overexpressers were not well balanced in various prognostic variables, he added.
Asked what he would advise Glaxo to do for renal cell carcinoma, Figlin said he "would ask them to put their resources elsewhere."
"The more subgroups you ask questions of, the greater likelihood — just on a statistical basis — that you'll find one with a positive result, independent of that effect being real," said Figlin.
— Chris Womack ([email protected])