[Edaily Reporter Minji Son ] #Cellbion Co., Ltd.’s prostate cancer radiopharmaceutical candidate “Pocubotide Satetrasetate” (Lu-177-DGUL) is once again drawing attention for its existing clinical results. This comes as it has belatedly come to light that an objective response rate (ORR) higher than the previously disclosed representative figure was observed in a patient group with lesions large enough to be measured via imaging. Although no new clinical results have been added, the fact that the figures vary depending on the analysis population appears to have influenced market interpretation.

According to Cellbion Co., Ltd on the 9th, in the domestic Phase 2 clinical trial of Focubotide, the objective response rate (ORR) was 35.9% among 28 of the 78 patients in the overall population evaluable for efficacy. The ORR is the percentage of patients who achieved a complete response (CR), in which the tumor has completely disappeared, or a partial response (PR), in which the tumor has shrunk by a certain threshold or more. Under RECIST v1.1, the criteria for evaluating responses in solid tumors, a PR is defined as a reduction of at least 30% in the sum of the diameters of measured target lesions compared to pre-treatment levels.

Following the announcement of Phase 2 topline results (key clinical findings) in September of last year, Cellbion Co., Ltd disclosed an ORR of 35.9% for the Full Analysis Set (FAS) in its announcement on December 12 of the same year regarding the receipt of the Clinical Study Report (CSR). Consequently, the market accepted this figure as a representative clinical achievement for Forqubotide.

However, market attention shifted again when it became known that, in addition to the previously reported key figure, the ORR for the subgroup of patients with measurable lesions had also been evaluated. Among the 57 patients in this subgroup, 27 demonstrated a complete response (CR) or partial response (PR), resulting in an ORR of 47.4%. This means that approximately half of the patients analyzed met the response criteria, exceeding the previously disclosed figure for the full analysis set.

The overall evaluation set may include patients who do not have lesions measurable by RECIST criteria. Since response assessment methods differ—for example, the PR category is not applied to patients with only non-measurable lesions—the ORR varies depending on which patient group is used as the denominator.

However, RECIST v1.1 provides guidelines stating that clinical trials using ORR as a primary endpoint may include only patients with measurable lesions prior to the start of treatment. Accordingly, it is believed that Cellbion Co., Ltd.’s clinical results have been re-examined after it was revealed that analyzing only this specific patient subgroup yielded a higher response rate than previously reported figures.

“Reevaluation” of Figures Hidden in Competitors’ Announcements

Interest in Cellbion Co., Ltd’s Poqubotide has grown even further following the announcement of the U.S. Phase 2a clinical trial results for “FC705,” a prostate cancer treatment candidate from FutureChem Co., Ltd.(220100).

FutureChem Co., Ltd. recently announced that, according to the top-line analysis of the U.S. Phase 2a clinical trial for FC705, 7 out of 18 patients with measurable lesions responded, resulting in an ORR of 38.9%. There were 5 complete responses (CR) and 2 partial responses (PR).

On the 23rd of last month, when these results were announced, the market reacted positively to FutureChem Co., Ltd.’s clinical trial. Consequently, the company’s stock price rose 29.91% during regular trading hours, closing at the daily upper limit of 8,990 won. Investor sentiment for Cellbion Co., Ltd. also improved in the wake of attention drawn to the fact that its ORR in the measurable lesion group—using the same evaluation criteria—was 47.4%.

A biotech industry official analyzed, “There were instances in the market where FutureChem Co., Ltd.’s 38.9% and Cellbion Co., Ltd.’s 35.9% were treated as comparable figures based on the same criteria,” adding, “Once it became clear that, when the scope of the analysis is aligned, the figures should be compared to Cellbion Co., Ltd.’s 47.4%, investors’ perceptions seem to have shifted.”

Even when compared to the results of Novartis’s commercially available prostate cancer treatment “Flubicto,” FutureChem demonstrated numerical competitiveness in some evaluation metrics. In particular, the clinical data based on the PCWG3-modified RECIST v1.1 criteria—which reflects the characteristics of prostate cancer—is noteworthy.

In the global Phase 3 “VISION” trial for Flubicto, as presented in the U.S. prescribing information, the ORR for measurable lesions under the PCWG3-modified RECIST criteria was 49%. By the same criteria, Cellbion Co., Ltd’s Poqubotide recorded a numerically higher ORR of 54.4%.

PCWG3-modified RECIST combines the standard RECIST criteria—which assess changes in the size of soft tissue lesions—with the evaluation of bone metastasis progression. It evaluates treatment response by reflecting the characteristics of prostate cancer, in which bone metastasis plays a significant role.

Pocubotide Preparing for Phase 3 Clinical Trial… First Dose Yet to Be Administered

Pocubotide is a radiopharmaceutical that targets prostate-specific membrane antigen (PSMA), which is expressed on prostate cancer cells. It delivers radiation to cancer cells by binding the therapeutic radioisotope lutetium-177 to a substance that seeks out the target.

The Phase 2 trial in Korea was conducted on patients with metastatic castration-resistant prostate cancer who had failed standard treatment or for whom standard treatment was no longer feasible. Participants included Seoul National University Hospital, Bundang Seoul National University Hospital, Asan Medical Center, Chonnam National University Hwasun Hospital, and Gangnam Severance Hospital.

During patient selection, lesions confirmed as targets via PET scans using the diagnostic agent Ga-68-NGUL were identified. Subsequently, Pocubotide was administered intravenously at a dose of 200 mCi per session at 6-week intervals, for a maximum of six sessions. A total of 91 patients were enrolled and received the treatment, and 78 were included in the primary efficacy analysis.

The trial was designed as a single-arm study to evaluate the efficacy and safety of Poqubotide without a control group receiving a comparator drug. It was an open-label trial in which both patients and healthcare providers were aware of the administered drug, and for the primary efficacy assessment, an independent evaluator determined tumor response according to RECIST v1.1. Changes in prostate-specific antigen (PSA) levels were also monitored through blood tests.

The subsequent Phase 3 trial for Poqubotide focused on determining not only the tumor response rate but also the extent to which it can delay disease progression. Cellbion Co., Ltd received approval from the Ministry of Food and Drug Safety for its domestic Phase 3 trial plan last September. Patient enrollment for the Phase 3 clinical trial has not yet begun.

According to the approved protocol, 150 patients with metastatic castration-resistant prostate cancer will be randomized in a 1:1 ratio to the treatment group and the control group. The control group will receive optimal supportive care and standard therapy, while the treatment group will receive these plus Poqubotide. Poqubotide will be administered four times at 6-week intervals, with a maximum of six doses if additional criteria are met.

The primary endpoint is radiographic progression-free survival (rPFS), assessed via blinded, independent central review according to PCWG3-modified RECIST v1.1. The study will compare the time from radiographic disease progression or death between the two groups.