Cellectar Biosciences reported Tuesday that 80% of patients with a rare blood cancer evaluated in a pivotal study responded to the company’s iodine-based treatment, and it plans to apply to the FDA for approval later this year.
In the 55 patients with Waldenström macroglobulinemia included in the efficacy analysis, the major response rate was 56.4%. Cellectar said that beat its primary endpoint goal of a 20% major response rate.
However, the safety results, which included 65 patients, showed high rates of decreased blood cell counts, which the company said was “consistent with treatment of hematologic malignancies.” About 55% of patients experienced grade 4 thrombocytopenia — or lower-than-normal platelet counts — while approximately 45% of patients experienced grade 4 neutropenia, or abnormally low white blood cell counts. More than one-third of patients also experienced grade 3 or 4 anemia, according to safety data Cellectar shared with Endpoints News.
Cellectar said the difference in the number of patients included in the efficacy and safety analyses was due to several reasons, citing a “study protocol violation by investigator,” that patients had to reach a certain total body dose of radioactivity to be included in the efficacy analysis, patients dropping out as a result of adverse events, and travel required for the study.
The company’s shares $CLRB, which rose roughly 20% on Monday, were down about 21% on Tuesday. Cellectar is disclosing full data on Wednesday during an investor call.
The data cutoff was May 31, according to the company.
Cellectar is developing a small molecule radiopharmaceutical called iopofosine I 131 to treat patients with Waldenström macroglobulinemia who have been previously treated. The drug’s goal is to deliver radioactive iodine to lipid rafts found in tumors, which are different from ones in normal cells, in order to kill the cancer cells.
With the data from its Phase 2 CLOVER WaM study, Cellectar said it plans to submit an application to the FDA by the end of the year and ask for priority review since its drug has a fast track designation.
Patients included in the study received a median of four prior treatment regimens, and around one-quarter were refractory to all available treatments, including a BTK inhibitor, an anti-CD20 antibody and chemotherapy, Cellectar said.
The patient population that Cellectar hopes to treat is small. “We see approximately 4,700 patients in the US requiring 3rd line or greater therapy with more than 900 new patients entering this line of therapy annually,” Cellectar told Endpoints. “We also believe based on claims data that there are approximately 1,000 patients that have exhausted prevalent treatment options.”
According to Cellectar, a large proportion of patients with later-line Waldenström macroglobulinemia are retreated with treatments they’ve already undergone or they receive therapies that aren’t FDA-approved for the blood cancer.
Cellectar announced Monday that it raised $19.4 million from warrants, and it could net up to another $73.3 million if investors exercise more warrants.