Analysis of tumor growth rate may be a valuable additional efficacy parameter to consider in patients with radioiodine-refractory differentiated thyroid cancer being treated with sorafenib, according to the results of a subanalysis of the phase III DECISION study (abstract 6015) presented at the 2015 American Society of Clinical Oncology (ASCO) Annual Meeting, held May 29 to June 2, in Chicago.
Sorafenib was approved for the treatment of radioactive-iodine refractory differentiated thyroid cancer in 2013 based on the results of the DECISION study, which found that sorafenib significantly improved progression-free survival and overall response rates compared with placebo.
In the trial, at disease progression, patients assigned to placebo were allowed to switch to open-label sorafenib (n = 150), and those assigned sorafenib were allowed to continue receiving the drug (n = 55).
For this subanalysis, presented as a poster by Christian Kappeler, of Bayer Pharma AG, Berlin, Germany, tumor growth rate was considered as an additional clinical parameter to compare treatment effects during double-blind treatment and open-label treatment, especially for placebo randomized patients who started sorafenib after prior progression.
During the double-blind portion of the trial, patients assigned sorafenib had a negative early tumor growth rate, which then increased, and patients assigned placebo generally had an increase in tumor size.
“The data showed that the treatment effect on tumor lesions in terms of early tumor growth at the start of sorafenib treatment was similar for sorafenib-arm patients during double-blind treatment and for placebo-arm patients after prior progression during open-label sorafenib treatment,” Kappeler said. “Early [tumor growth rate] during sorafenib treatment was decreased by a similar extent both for patients randomized to sorafenib and patients randomized to placebo who crossed over to receive open-label sorafenib after disease progression.”
Among patients who started on placebo and then crossed over to sorafenib, there was a negative early tumor growth rate and a lower late tumor growth rate compared with growth seen during double-blind treatment. For those patients assigned to sorafenib who continued on treatment, there was a positive but similar tumor growth rate during the late double-blind portion of the study and the open-label portion.
Late tumor growth rate at the time of progression was lower for patients receiving double-blind or open-label treatment with sorafenib than for those initially assigned to placebo, which suggests that despite reaching disease progression there was still partial suppression of tumor growth in patients randomized to sorafenib relative to tumor growth in patients receiving placebo, Kappeler said.
In a discussion of the results of the study Robert Haddad, MD, of Dana-Farber Cancer Institute said that tumor growth rate as used in this analysis was an “interesting parameter but with limited clinical application currently.”
This study was supported by Bayer HealthCare Pharmaceuticals and Onyx Pharmaceuticals.