“Stage 4 colorectal cancer is a malignant condition that spreads to other organs such as lymph nodes, liver, and lungs, which most existing treatment methods fail to address. The survival period without tumor metastasis was just over two months with standard treatments, but the new drug candidate being developed by STCube has shown over 4.4 months in clinical trials. This is why global big pharma companies are taking an interest in our treatment substance.”
On 15th (local time), Yoo Seung-han, CEO of STCube USA and head of research and development, participating in the JP Morgan Healthcare Conference (JPM2025) held in San Francisco, stated, “The colorectal cancer treatment ’Nelmastobart’ currently under development is in discussions for technology exports with 10 big pharma companies at this JPM, following the BioUSA (Bio International Convention) last June.”
Traditionally, the medical community has attributed the reason cancer cells spread in our bodies to proteins called 'PD-1' and 'PD-L1.' Cancer cells use this substance to disguise themselves as normal cells, avoiding attacks from immune cells (T cells). However, there are still many patients who do not see therapeutic effects from PD-1 and PD-L1 immune checkpoint inhibitors.
Founded in 1989, STCube gained industry attention for being the first in the world to discover a new immune checkpoint protein, BTN1A1. The immuno-oncology development company STCube is focused on new treatments for colorectal cancer. CSO Yoo noted, “We developed Nelmastobart, an immuno-oncology candidate targeting BTN1A1, five years ago. After completing preclinical studies at the MD Anderson Cancer Center in the U.S., we entered Phase 1 clinical trials in 2018.”
CSO Yoo is a high school classmate of Jeong Hyun-jin, the founder of STCube, and an expert who led the radiation therapy drug development division at the National Cancer Institute (NCI) in the U.S. He joined STCube after leaving NCI in 2013, sharing a commitment with CEO Jeong to develop new immuno-oncology drugs. Since 2013, he has been leading clinical trials and research and development at STCube Pharmaceuticals, based in the U.S. state of Maryland.
According to the World Health Organization (WHO), colorectal cancer is the third most common cancer worldwide, following liver and bile duct cancers, and ranks second in mortality rates after lung cancer. South Korea has the highest incidence rate of colorectal cancer among 184 countries surveyed by the WHO. While early detection leads to a high survival rate, the symptoms are not apparent, leading to late-stage diagnoses and earning it the nickname 'the silent killer.'
The biggest enemies of colorectal cancer are 'recurrence' and 'metastasis.' Colorectal cancer has a high recurrence rate and a significant risk of metastasizing to other organs, making it an intractable solid tumor. Liver metastasis occurs in 70% of patients, drastically reducing survival rates.
Currently, there is no appropriate treatment. Among the microsatellite stable (MSS) patient group, which accounts for approximately 90% of colorectal cancer patients, treatment effects from standalone immuno-oncology drugs are nearly nonexistent, particularly in the case of MSS metastatic colorectal cancer. American company Merck (MSD), known for developing the prominent immuno-oncology drug Keytruda, and Bristol-Myers Squibb (BMS) have also jumped into developing metastatic colorectal cancer treatments, but they failed to demonstrate efficacy. Presently, there are no available treatments for the vast majority of colorectal cancer patients.
According to STCube, Nelmastobart has broken the record set by existing standard treatments in Phase 1 trials.
The company's earlier Phase 1b trial involved 12 stage 4 colorectal cancer patients where Nelmastobart was administered in combination with Swiss Roche's standard third-line treatment, Xeloda (active ingredient capecitabine). As a result, the progression-free survival (PFS) period—duration without progression or metastasis of cancer—was recorded at 4.4 months.
CSO Yoo explained, “This figure is more than double that of existing treatments, where the PFS is only two months,” adding, “The significantly lower toxicity of Nelmastobart compared to other treatments has been beneficial in extending survival time.” The median PFS is expected to be revealed at the ASCO GI (American Society of Clinical Oncology Gastrointestinal Cancers Symposium 2025) held in San Francisco on the 23rd.
Additionally, among the 12 patients, two showed partial response (PR) with tumor reductions of less than half, while 10 exhibited stable disease (SD) with no disease progression. The disease control rate (DCR), indicating the proportion of patients with delayed disease progression, was 100%. CSO Yoo noted, “The DCR for Keytruda was around 41-69%, which shows a significant difference compared to our recorded 100%,” and he emphasized, “Although it’s still Phase 1, it surpasses the records of existing treatments.”
CSO Yoo visited this JPM with Professor Lee Soo-hyun from Korea University Anam Hospital's Department of Oncology, who led the Nelmastobart trials, to provide a more detailed explanation of the clinical results during meetings with big pharma. STCube is currently conducting Phase 2 trials with 35 patients at Korea University Anam Hospital, which is expected to be completed within this year.
CSO Yoo remarked, “As the development of colorectal cancer treatments has faced successive failures, it was essentially seen as an impossible area within the industry,” and added, “However, as the clinical results for Nelmastobart continue to emerge, the reactions from big pharma are changing.” He noted, “Several big pharma companies currently focused on developing anticancer drugs have shown interest, and discussions on technology exports are ongoing.”