Blocking FGFR Signaling Supercharges Immunotherapy in Hard-to-Treat Colorectal Cancer

Immunotherapy has transformed the treatment landscape for many cancers, but one of the most common malignancies worldwide has stubbornly resisted the revolution. Colorectal cancer, which claims hundreds of thousands of lives each year, responds to immune checkpoint blockade only in the small subset of tumors classified as microsatellite instability-high. The vast majority of patients carry microsatellite stable (MSS) tumors, and for them, drugs that unleash T cells against PD-1 have delivered disappointing results. A new study published in BMC Cancer by Zhou Shang, Changqing Jing and colleagues offers a potential way past this immunological wall, showing that inhibiting the fibroblast growth factor receptor (FGFR) pathway can dramatically reshape the tumor immune environment and amplify the effects of PD-1 blockade in colorectal cancer models.

The research, a collaboration between teams at Shandong Provincial Hospital Affiliated to Shandong First Medical University in China and Science for Life Laboratory at Uppsala University in Sweden, focused on a signaling axis that has long been implicated in cancer progression but rarely examined through an immunological lens. The FGFR family of receptor tyrosine kinases, comprising FGFR1 through FGFR4, regulates cell proliferation, survival, migration and differentiation. When these receptors are activated by their ligands or altered by genetic changes, they can drive tumor growth and, as mounting evidence suggests, help cancers hide from the immune system. The researchers set out to determine whether silencing this pathway in colorectal cancer could strip away one layer of that camouflage.

The team’s experimental strategy combined laboratory models with large-scale genomic data. In murine colorectal cancer models, they tested FGFR pathway inhibition alone and in combination with antibodies that block PD-1, the checkpoint receptor that exhausted T cells use to disengage from tumor cells. In parallel, they built in vitro co-culture systems in which T cells and tumor cells interact under controlled conditions, allowing them to measure precisely how FGFR3 blockade changes T cell activation. To connect these mechanistic findings to human disease, they performed RNA sequencing and bioinformatic analyses, including an evaluation of The Cancer Genome Atlas (TCGA), one of the largest publicly available collections of tumor transcriptomic and clinical data.

The results point to a coherent immunological mechanism. When the researchers combined FGFR inhibition with PD-1 blockade, they observed a significant reduction in T cell exhaustion, the dysfunctional state that renders tumor-infiltrating lymphocytes unable to kill their targets. Exhausted T cells express inhibitory receptors, lose their cytotoxic potency and secrete diminished amounts of inflammatory mediators. By reversing this state, the combination treatment appeared to reinvigorate the cellular arm of the antitumor immune response. Equally striking was the effect on myeloid cells: the treatment promoted macrophage repolarization toward an antitumor phenotype. Macrophages are notoriously plastic; within tumors they often adopt a pro-tumor, immunosuppressive identity that suppresses T cells and promotes tissue invasion. Shifting them back toward an inflammatory, tumor-fighting state represents a second, complementary lever on the immune microenvironment.

Transcriptomic profiling provided a molecular explanation for these cellular observations. RNA sequencing revealed that combined FGFR inhibition and PD-1 blockade upregulated immune-related pathways and activated immune-stimulatory genes, effectively rewiring the tumor’s gene expression program toward one that recruits and supports immune attack. In the co-culture experiments, the most direct functional readout came from FGFR3-specific monoclonal antibody treatment, which enhanced the release of interferon-gamma following PD-1 blockade. Interferon-gamma is a signature cytokine of activated T cells and natural killer cells, and its production is a hallmark of productive antitumor immunity. The finding that a monoclonal antibody against a single receptor, FGFR3, could boost this cytokine response when paired with checkpoint blockade suggests that the effect is not a diffuse consequence of general growth factor withdrawal but a targeted immunological shift.

The clinical relevance of these findings was reinforced by the TCGA analysis. The researchers found that high FGFR3 expression correlates with worse prognosis in colorectal cancer patients, linking the receptor’s activity to patient outcomes in a large human cohort. This epidemiological signal matters because it suggests that FGFR3 is not merely a passenger in colorectal tumors but a biologically meaningful participant whose expression marks aggressive disease. It also provides a potential biomarker: patients whose tumors express high levels of FGFR3 might be the ones most likely to benefit from a combination strategy that includes FGFR inhibition, an approach that aligns with the broader movement toward biomarker-guided immunotherapy combinations.

The significance of the work lies in the specific problem it addresses. Microsatellite stable colorectal cancer has been described as a cold tumor type, characterized by low mutational burden, sparse T cell infiltration and an immunosuppressive stroma. Checkpoint inhibitors work best when pre-existing antitumor T cells are present but restrained; in MSS colorectal cancer, that substrate is often missing. Strategies to convert cold tumors into hot ones, including oncolytic viruses, radiation, chemotherapy and targeted agents, have produced mixed results. The new study adds FGFR inhibition to this arsenal, and its dual mechanism, reducing T cell exhaustion while repolarizing macrophages, targets two distinct pillars of immune suppression simultaneously. That combination of effects may explain why the pairing with PD-1 blockade produced such pronounced immunological changes in the models.

It is worth placing the findings in the context of existing FGFR-directed therapeutics. Several FGFR inhibitors, mostly small-molecule kinase inhibitors such as erdafitinib and pemigatinib, are already approved for other cancers with FGFR alterations, including urothelial carcinoma and cholangiocarcinoma. The prospect of extending this drug class into colorectal cancer, not as a standalone cytotoxic agent but as an immunomodulatory partner for checkpoint blockade, represents a conceptual repurposing. The Swedish-Chinese team’s use of an FGFR3-specific monoclonal antibody in vitro also highlights an alternative modality: receptor-specific antibodies may offer cleaner target engagement than broad-spectrum kinase inhibitors, potentially limiting the toxicities that have complicated FGFR-targeted therapy, such as hyperphosphatemia and ocular side effects.

As with any preclinical study, important caveats apply. The work was conducted in murine models and in vitro co-culture systems, which, however sophisticated, cannot fully reproduce the complexity of human colorectal tumors, including their heterogeneous microbiomes, stromal architectures and evolutionary histories. The authors themselves frame their findings as providing a rationale for further investigation rather than as proof of clinical efficacy. Translating the combination into patients will require careful dose-finding, attention to the safety of adding FGFR inhibition to immunotherapy, and clinical trials designed to test whether the biomarker signal from TCGA, high FGFR3 expression predicting poor prognosis, also predicts benefit from the combination. The study was approved by the Review Committee of Shandong First Medical University Affiliated Provincial Hospital and conducted in compliance with ARRIVE 2.0 reporting guidelines, and the authors declare no competing interests.

Nevertheless, the study adds an important piece to one of oncology’s most pressing puzzles: how to make immunotherapy work for the patients who currently derive no benefit from it. By demonstrating that FGFR pathway inhibition reduces T cell exhaustion, repolarizes macrophages, upregulates immune-stimulatory genes and enhances interferon-gamma release in the presence of PD-1 blockade, the researchers have articulated a mechanistically grounded rationale for a new combination strategy in MSS colorectal cancer. If subsequent studies in patients confirm what the mouse models and genomic analyses suggest, the FGFR axis, long studied as a driver of tumor growth, may find a second career as a gatekeeper of antitumor immunity, and its inhibition may help open the door that checkpoint inhibitors alone have been unable to unlock for the majority of colorectal cancer patients.

Subject of Research: FGFR pathway inhibition combined with PD-1 blockade to enhance antitumor immunity in microsatellite stable colorectal cancer

Article Title: FGFR pathway inhibition enhances PD-1 blockade and modulates antitumor immunity in colorectal cancer models

Article References: FGFR pathway inhibition enhances PD-1 blockade and modulates antitumor immunity in colorectal cancer models. (n.d.). https://doi.org/10.1186/s12885-026-17105-9

Image Credits: AI Generated

DOI: 10.1186/s12885-026-17105-9

Keywords: colorectal cancer, FGFR signaling, PD-1 blockade, immunotherapy, microsatellite stable, T cell exhaustion, macrophage repolarization, interferon-gamma, TCGA, combination therapy, immune checkpoint blockade, tumor microenvironment