Trabectedin OS Data Unclear in Phase III Sarcoma Study

Silas Inman @silasinman
Published: Saturday, Sep 26, 2015

Dr Shreyaskumar R. Patel

Shreyaskumar R. Patel, MD

The final analysis of phase III data for trabectedin (Yondelis) were consistent with interim results by showing a lack of improvement for the primary endpoint of overall survival (OS) in patients with advanced soft tissue sarcoma, according to data presented at the 2015 European Cancer Congress (ECC).1

After a 21-month follow-up, the median OS with trabectedin was 13.7 months compared with 13.1 months with dacarbazine (HR, 0.93; 95% CI, 0.75-1.15; P = .492). The median progression-free survival (PFS) with trabectedin was 4.2 versus 1.5 months with dacarbazine (HR, 0.55; 95% CI, 0.44-0.70; P <.001).

In the data presented by Shreyaskumar R. Patel, MD, the lack of OS was explained by a 47% longer median time to initiation of subsequent therapies in patients treated with trabectedin. The next therapy was initiated after a median of 6.8 months in those receiving trabectedin versus 3.5 months for those in the dacarbazine arm (HR, 0.53; P <.0001).

"Sensitivity analyses of OS showed a consistent favorable trend for the trabectedin group, supporting a potential confounding effect of additional post-study therapies, which were instituted earlier in the dacarbazine group," Patel, from the MD Anderson Cancer Center, and colleagues wrote in the abstract. 

In the open-label trial, 518 patients were randomized in a 2:1 ratio to 1.5 mg/m2 of trabectedin (n = 345) or 1.0 g/m2 of dacarbazine (n = 173) once every 3 weeks until disease progression or unacceptable toxicity. Patients in the trabectedin arm received 20 mg of IV dexamethasone as a premedication. The study enrolled participants across a variety of soft tissue sarcoma histologies, including leiomyosarcoma, nonuterine, uterine, liposarcoma, dedifferentiated, myxoid, and pleomorphic.

In the dacarbazine arm patients received a median of 2 treatment cycles versus 4 in the trabectedin group. The median duration of response with trabectedin was 6.5 months compared with 4.2 months with dacarbazine (HR, 0.47; P = .14). The objective response rates were 9.9% versus 6.9% and the clinical benefit rate (response plus stable disease rate) was 34% and 19%, for trabectedin and dacarbazine, respectively.

OS findings were consistent across a planned subgroup analysis. In a multivariate analysis, OS was improved by trabectedin for patients who received only 1 prior line of chemotherapy versus ≥2 and for those with an ECOG PS of 0 versus 1 (P <.05).

"Some patients get extremely good responses and durable stability of their disease [with trabectedin], sometimes lasting 4 to 5 years with metastatic sarcomas," lead investigator George D. Demetri, MD, director, Center for Sarcoma and Bone Oncology at Dana Farber Cancer Center, told OncLive. "The problem is that we don't know who those people are who will get the extraordinary benefits."

Approximately 70% of patients in each group went on to receive additional treatment. During the course of the trial, the angiogenesis inhibitor pazopanib (Votrient) was approved for patients with soft tissue sarcoma—an event that may have confounded the OS analysis, according to Demetri. In fact, 18% of patients in the trabectedin arm received subsequent pazopanib compared with 28% in the dacarbazine arm.

"It was a difficult study to implement, patients once randomized did not have the option to crossover to the other therapy if the disease progressed," Demetri explained. "Overall survival is a difficult endpoint, because it measures not just what you're doing with the patient in that particular trial but also whatever happens to the patient when the tumor gets worse and the patient comes off the study. Overall survival is a controversial endpoint in our world of sarcoma management."

In data published in the Journal of Clinical Oncology in mid-September,2 the most commonly reported all-grade adverse events (AEs) with trabectedin versus dacarbazine were nausea (73% vs 49%), fatigue (67% vs 51%), neutropenia (49% vs 29%), increased ALT levels (45% vs 6%), vomiting (44% vs 21%), anemia (39% vs 29%), constipation (36% vs 28%), increased AST levels (35% vs 5%), and diarrhea (34% vs 23%).

Grade 3 AEs with the highest frequency in the trabectedin arm were increased ALT levels (25% vs 1%), neutropenia (21% vs 11%), anemia (14% vs 11%) and increased AST levels (12% vs 0%). Sixteen percent of patients receiving trabectedin had grade 4 neutropenia compared with 10% in the dacarbazine group.

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