A groundbreaking discovery by West China Hospital researchers reveals why small cell lung cancer resists immunotherapy - and points to a potential solution using existing drugs.
Table of Contents
- The Discovery: A Hidden Barrier Inside Tumors
- Understanding Small Cell Lung Cancer
- How BVG Blocks Immune Cells
- A Drug That Already Exists
- Implications for Cancer Treatment
- Sources
The Discovery: A Hidden Barrier Inside Tumors {#discovery}
On May 7, 2026, researchers from West China Hospital of Sichuan University published a landmark study in Cell, one of the world’s most prestigious scientific journals. The team, led by Professor Chen Chong, Professor Liu Yu, Associate Professor Na Feifei, and Professor Zhang Yan, discovered a previously unknown vascular structure in neuroendocrine tumors that acts as a physical barrier preventing immune cells from entering and attacking the cancer.
This structure, named the “Blood-Brain Barrier-like Vascular Gate” (BVG), explains why small cell lung cancer (SCLC) - one of the deadliest forms of lung cancer - responds so poorly to immunotherapy, despite recent advances in cancer treatment.
The discovery challenges conventional wisdom in cancer biology. While most tumor blood vessels are leaky and disorganized, the BVG exhibits tight junctions between endothelial cells, a thickened basement membrane, and dense pericyte coverage - features remarkably similar to the blood-brain barrier that protects our central nervous system.
Understanding Small Cell Lung Cancer {#understanding}
Small cell lung cancer accounts for approximately 15-20% of all lung cancer cases, making it one of the most common neuroendocrine tumors. It is notoriously aggressive, spreading rapidly throughout the body with a devastating five-year survival rate of less than 10%.
SCLC has long been classified as a “cold tumor” - meaning it has low levels of immune cell infiltration. This characteristic makes it particularly resistant to immune checkpoint inhibitors, the revolutionary cancer treatments that have transformed outcomes for many other cancer types. Until now, the underlying mechanism for this resistance remained a mystery.
The West China Hospital research team’s identification of BVG provides the missing piece of this puzzle. The blood-brain barrier-like structure effectively creates a fortress around the tumor, preventing T cells from penetrating and mounting an immune attack.
How BVG Blocks Immune Cells {#mechanism}
The researchers traced the formation of BVG to a specific molecular pathway. They discovered that SCLC tumor cells express high levels of a transcription factor called ASCL1, which regulates the secretion of a protein called IGFBP5. This protein then transports IGF1 to endothelial cells, where it activates the IGF1 receptor (IGF1R) signaling pathway.
This signaling cascade triggers the formation of the BVG structure, with its characteristic tight junctions and barrier properties. The result is a vascular gate that efficiently blocks T cells from entering the tumor microenvironment.
Using advanced imaging techniques and animal models, the team demonstrated that mice with intact BVG showed poor T cell infiltration into tumors and minimal response to immunotherapy. However, when the researchers disrupted the ASCL1-IGFBP5-IGF1R axis, the BVG structure collapsed, allowing immune cells to flood into the tumor and dramatically improving immunotherapy effectiveness.
A Drug That Already Exists {#potential}
Perhaps most exciting for patients is the discovery that an existing drug may be able to break down this barrier. IGF1R inhibitor OSI-906 (linisertib), which has already been tested in clinical trials and shown to have a good safety profile, was found to significantly enhance immunotherapy response in preclinical models.
OSI-906 previously failed as a standalone treatment for SCLC in clinical trials, but the new research suggests it may have a second life as an immunotherapy sensitizer. When combined with immune checkpoint inhibitors, OSI-906 could potentially unlock the tumor’s defenses and allow immunotherapy to work effectively.
This finding is particularly valuable because the drug has already undergone extensive safety testing, potentially accelerating the timeline for clinical application. The West China Hospital team’s discovery transforms a “failed” drug into a promising combination therapy candidate.
Implications for Cancer Treatment {#implications}
The discovery of BVG represents a paradigm shift in our understanding of tumor vasculature and immune evasion. Traditional approaches to tumor blood vessels have focused on “normalization” - reducing the abnormal permeability of tumor vessels to improve drug delivery. The new findings suggest that for neuroendocrine tumors, the opposite approach may be needed: deliberately disrupting the barrier to allow immune cell entry.
The research also opens new avenues for treating other neuroendocrine cancers beyond SCLC. The BVG structure was found in various neuroendocrine neoplasms, suggesting the findings could have broad applications across this challenging class of tumors.
For the millions of patients affected by aggressive neuroendocrine cancers, this research offers new hope. The identification of BVG as a targetable mechanism of immunotherapy resistance provides a clear path forward for developing more effective treatments. Clinical trials combining IGF1R inhibitors with immunotherapy could begin relatively quickly, given the existing safety data for these drugs.
The study was a collaborative effort involving researchers from West China Hospital’s State Key Laboratory of Biotherapy, Cancer Center, and Lung Cancer Center, along with teams from the Affiliated Hospital of Chengdu University of Traditional Chinese Medicine. Academician Wei Yuquan and Academician Bian Xiuwu provided important guidance for the research.