Maintenance therapy with enzastaurin, an experimental agent directed against B-cell malignancies, did not improve disease-free survival among patients with high-risk diffuse large B-cell lymphomas following complete responses to chemotherapy with rituximab.
In a randomized, double-blind trial, after a median follow-up of 48 months, the hazard ratio for disease-free survival with enzastaurin vs. placebo, the primary endpoint, was 0.92 (P = .541), reported Dr. Michael Crump of Princess Margaret Cancer Centre in Toronto, and colleagues.
“The risk of treatment failure, however defined, is likely to be different in the subpopulation of patients who achieve remission after that treatment. Furthermore, identifying the value of specific biomarkers in predicting therapeutic response to novel targeted agents may be necessary in guiding future trials within defined subgroups of patients with DLBCL,” they wrote in the study, published online May 23 in Journal of Clinical Oncology.
Enzastaurin is a selective inhibitor of the protein kinase C-beta isoform (PKC-beta) expressed in both normal and malignant B cells. It has been shown to decrease tumor proliferation and induced apoptosis in cancer cells, and has been shown to have activity against relapsed or refractory DLBCL, mantle cell lymphoma, and follicular lymphoma, the authors explained.
Dr. Crump and colleagues conducted a phase III study to determine whether enzastaurin could be effective as maintenance therapy in patients with DLBCL at high risk for relapse after having had complete responses to first-line therapy with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP).
They enrolled 758 patients with stage II bulky DLBCL or stage III-IV disease who had three or more International Prognostic Index risk factors at diagnosis, and who had achieved either a confirmed or unconfirmed complete response after six to eight cycles of R-CHOP.
The patients were randomly assigned on a 2:1 basis to receive either oral enzastaurin 500 mg daily or placebo for 3 years, or until disease progression or unacceptable toxicity,
As noted, there was no significant difference in DFS with the active drug vs. placebo. In addition, in correlative analyses looking for biomarkers of response by cell of origin (i.e., germinal-center or non–germinal-center B cell) or by PKC-beta protein expression, the authors found no significant associations with either DFS or overall survival.
Enzastaurin was generally safe, with minor and manageable adverse events. More patients in the enzastaurin arm had episodes of QTc prolongation, but these did not require discontinuation of the drug.
Dr. Crump and coauthors disclosed consulting, advising, research funding and other relationships with various companies, including Eli Lilly. Five coauthors are Lilly employees.