Researchers at the German Cancer Research Center (DKFZ) and the Heidelberg Institute for Stem Cell Technology and Experimental Medicine (HI-STEM) have identified a mechanism that may explain why a particularly aggressive subtype of colorectal cancer can escape immune surveillance. Their findings indicate that activation of the WNT signaling pathway does more than stimulate uncontrolled tumor growth: it also reshapes the surrounding tissue in a way that limits the arrival of immune cells. By reducing production of the signaling molecule CCL20, WNT-activated cancer cells appear to create an immunologically quieter environment in which malignant transformation can proceed with less resistance from the body’s defenses.
Colorectal cancer is diagnosed in approximately 55,000 people in Germany each year. Around one quarter of these cancers arise from serrated lesions, a distinctive type of colorectal polyp that can serve as a precursor to malignancy. Many of these lesions carry activating mutations in the BRAF gene. Although BRAF mutations are also found in other cancers, their presence in serrated colorectal lesions is associated with a tumor subtype that often develops aggressive biological features and responds poorly to available treatments. The molecular events that convert these precursor lesions into invasive cancer, however, have remained incompletely understood.
The new study places WNT signaling at the center of this transformation. WNT proteins regulate a fundamental communication network involved in cell proliferation, tissue organization, stem-cell maintenance, and embryonic development. In healthy intestinal tissue, WNT activity is carefully controlled because the pathway helps maintain the rapidly renewing lining of the gut. When this signaling becomes persistently activated in a genetically altered cell, it can promote the expansion of abnormal cell populations and disrupt the architecture of the tissue. The DKFZ and HI-STEM researchers found that, in the context of BRAF-mutant colorectal lesions, WNT activation helps initiate the transition from a premalignant state to a malignant tumor.
To follow this process, the investigators combined genetically engineered mouse models with three-dimensional intestinal organoids and single-cell analysis. Organoids are laboratory-grown structures derived from stem or tumor cells that reproduce several features of intestinal tissue, including aspects of its organization and response to signaling cues. Single-cell technologies allowed the researchers to examine gene activity in individual tumor and neighboring cells rather than averaging molecular signals across an entire tumor. This approach revealed that WNT activation was accompanied by extensive remodeling of the tumor microenvironment, the complex mixture of immune cells, connective-tissue cells, blood vessels, and signaling molecules that surrounds and influences cancer cells.
One of the most important changes involved CCL20, a chemokine that helps guide immune-cell movement. Chemokines are soluble signaling proteins that establish molecular gradients in tissues, effectively creating directional cues that immune cells can follow. CCL20 is recognized by the receptor CCR6 on certain immune-cell populations and can contribute to the recruitment and positioning of immune cells in epithelial tissues. In the models studied by the researchers, WNT-activated tumor cells produced markedly less CCL20 than their less transformed counterparts. The resulting reduction in chemokine signaling was associated with a decrease in immune-cell entry into the developing tumor.
This finding suggests that immune evasion begins during the earliest stages of malignant transformation rather than emerging only after a fully established tumor has developed. Instead of simply growing faster, the altered cells appear to modify the biological conditions around them. By weakening a signal that helps attract immune cells, they may reduce the likelihood that potentially cancer-fighting cells will encounter the emerging tumor. The result is not necessarily a complete absence of immune activity, but a tumor microenvironment with fewer immune cells and less effective immune surveillance. Such an environment can give genetically abnormal cells additional time to survive, multiply, and acquire further malignant properties.
The researchers also tested whether restoring the missing signal could influence tumor behavior. In experimental models, re-establishing CCL20 production significantly slowed tumor growth. This result supports the idea that the chemokine is not merely a passive marker of tumor development but may play a functional role in controlling the interaction between transformed cells and the immune system. It also demonstrates how a molecular change inside cancer cells can produce consequences at the level of the entire tissue. The study does not show that CCL20 restoration is ready for use as a treatment, but it identifies the signaling axis as a possible point of intervention for future research.
The work further connects two major features of BRAF-mutant colorectal cancer: abnormal growth signaling and immune escape. BRAF is part of the MAPK signaling cascade, a pathway that transmits signals controlling cell division and survival. WNT signaling operates through a separate but highly interconnected regulatory system, and cancer cells frequently exploit cooperation between these pathways. In the tumors examined in this study, WNT activity appears to provide the crucial step that drives BRAF-mutant precursor lesions toward malignancy while simultaneously altering their immune surroundings. This may help explain why tumors arising through the serrated pathway can behave differently from other forms of colorectal cancer, even when they develop in the same organ.
The findings point to WNT signaling as a potential therapeutic target, although significant obstacles remain. Several WNT-directed drugs are being evaluated in clinical development, but no WNT inhibitor has yet been approved as a cancer treatment. The pathway is essential for normal tissue maintenance, particularly in the intestine, raising concerns that systemic inhibition could damage healthy organs or produce unacceptable side effects. A more selective strategy might involve targeting abnormal WNT activity in tumors, interrupting cooperation between WNT and BRAF signaling, or combining WNT inhibition with immunotherapies. Restoring immune access to the tumor could, in principle, make cancer cells more visible or vulnerable to immune-based treatments, but this possibility must be tested in carefully designed preclinical and clinical studies.
The study provides a mechanistic explanation for how BRAF-mutated colorectal tumors may establish an immune-suppressed environment while they are still forming. It also illustrates the value of studying cancer as an evolving ecosystem rather than as a collection of isolated mutations. The researchers emphasize that the relationship between genetic alterations and immune function is central to understanding tumor aggressiveness. By showing that WNT-driven suppression of CCL20 can promote malignant transformation, the work offers a new framework for investigating serrated colorectal cancer and may eventually support combination treatments designed to target both the cancer cell’s growth circuitry and the immune environment that allows it to thrive.
Subject of Research: WNT-driven immune evasion and malignant transformation in BRAF-mutant colorectal cancer.
Article Title: WNT-driven immune evasion promotes malignant transformation of BRAF-mutant colorectal cancer.
Web References: https://doi.org/10.1053/j.gastro.2026.07.035
References: Manuel Mastel, Aitana Guiseris Martinez, Umberto Pozza, Jasmin Meier, Ioannis Chiotakakos, Sandra Jaun, Carolin Artmann, Gabriele Diamante, Nikolaos Georgakopoulos, Philipp Albrecht, Yvonne Petersen, Saskia Reuter, Barbara Schmitt, Michael Günther, Alexandra Thiran, Istiffa Nurfauziah, Ian Ghezzi, Kyanna S. Ouyang, Michael D. Milsom, Jens Puschhof, Nic G. Reitsam, Kim E. Boonekamp, Johannes Betge, Steffen Ormanns, Michael Boutros and Rene Jackstadt. “WNT-driven immune evasion promotes malignant transformation of BRAF-mutant colorectal cancer.” Gastroenterology, 2026. DOI: 10.1053/j.gastro.2026.07.035.
Keywords: colorectal cancer, BRAF mutation, WNT signaling, immune evasion, CCL20, tumor microenvironment, serrated lesions, cancer immunology, organoids, single-cell analysis, malignant transformation, colorectal cancer therapy
