New Study Uncovers Unexpected Side Effects of High-Dose Radiation Therapy

In a groundbreaking new publication in Nature, scientists at the University of Chicago Medicine Comprehensive Cancer Center reveal an unexpected paradox in radiation oncology that challenges long-standing assumptions about how radiotherapy influences metastatic cancer. Their research uncovers a phenomenon where high-dose radiation – instead of merely shrinking or controlling tumors – can paradoxically stimulate the growth of preexisting metastatic tumors located outside the irradiated field. This counterintuitive response, termed the “badscopal effect,” stands in stark contrast to the well-documented “abscopal effect,” where radiation triggers immune-mediated tumor regression at distant sites.

Radiotherapy has long been a cornerstone in the multimodal treatment of cancer, valued for its ability to destroy localized tumors through DNA damage and cellular apoptosis. Traditionally, its immunomodulatory impact was considered beneficial; radiation could often activate systemic anti-tumor immunity, resulting in the regression of untreated distant tumors – the abscopal effect. This phenomenon has fueled hope that radiation could be harnessed not just as a local weapon but as a systemic therapeutic agent to combat metastatic disease. However, real-world clinical outcomes have been inconsistent, particularly in patients with oligometastatic disease receiving stereotactic body radiotherapy (SBRT) combined with immunotherapy. Many patients fail to exhibit sustained systemic tumor control and even experience progression of untreated metastases.

The team led by Dr. Ralph Weichselbaum, a pioneering figure in radiation and cellular oncology, hypothesized that under certain conditions, high radiation doses might paradoxically facilitate tumor progression at unirradiated metastatic sites. This insight has profound implications for understanding treatment failures and guiding future therapeutic strategies. To rigorously explore this, researchers analyzed biopsies from patients enrolled in clinical trials where SBRT was administered alongside checkpoint inhibitors like pembrolizumab. Strikingly, they found that some untreated metastatic lesions grew post-radiation, signaling that radiotherapy might unwittingly signal and feed distant tumor expansion.

Delving deeper into the molecular mechanisms underlying this phenomenon, postdoctoral fellow Dr. András Piffkó and collaborators conducted gene expression profiling in irradiated tumor samples. Their analysis unveiled a significant upregulation of amphiregulin, a ligand for the epidermal growth factor receptor (EGFR), in tumor cells exposed to high-dose radiation. Amphiregulin’s binding to EGFR triggers phosphorylation cascades that promote cellular survival, proliferation, migration, and resistance to apoptosis—pathways well known for their contributions to tumor aggressiveness.

To substantiate the clinical observations, sophisticated animal models of lung and breast cancer metastasis were employed. These studies showed a marked dichotomy: while radiation curtailed the emergence of new metastatic foci, it simultaneously accelerated the growth kinetics of established metastatic tumors. This dual effect hinged on the induction of amphiregulin, which was markedly elevated both within the tumor microenvironment and systemically in the bloodstream after radiotherapy. Crucially, therapeutic interventions that blocked amphiregulin function—either through neutralizing antibodies or CRISPR-mediated gene knockout in tumor cells—successfully curtailed the growth of distant metastases, even outside the radiation field. The findings suggest amphiregulin is a critical molecular mediator of the badscopal effect.

Furthermore, the researchers uncovered a complex interplay between amphiregulin and the host immune system’s capacity to surveil and eliminate cancer cells. Elevated amphiregulin correlated with an increase in immunosuppressive myeloid cells, which are known to dampen anti-tumor immune responses. This immune cell population exhibits phenotypes that inhibit cytotoxic T cell activity and promote tumor tolerance. Prior work from the same group had demonstrated that ablating these myeloid subsets reduces metastatic burden; in contrast, amphiregulin expression appeared to skew myeloid cell differentiation towards an immunosuppressive state.

Another critical element involved the upregulation of CD47, a macrophage “don’t eat me” signal, in amphiregulin-high tumors following radiation. This molecular cloak impairs macrophage and myeloid cell phagocytic activity, enabling tumor cells to evade innate immune elimination. Collaborations with biochemistry experts led to the pivotal discovery that targeting both amphiregulin and CD47 concurrently, alongside radiotherapy, produced robust control over metastatic disease in preclinical models. This combinatorial strategy effectively counteracted the badscopal effect and restored systemic tumor suppression.

These results compel a paradigm shift in how radiotherapy is conceptualized and applied in oncologic care, particularly in the metastatic setting. Rather than viewing radiation as purely an immunostimulatory approach, clinicians and researchers must now consider its potential to induce tumor-promoting factors like amphiregulin that can subvert immune surveillance. Monitoring amphiregulin expression levels post-radiotherapy could serve as a biomarker to identify patients at risk for metastatic progression, guiding more personalized and adaptive treatment regimens.

The study’s authors are vigorously planning clinical trials that integrate amphiregulin and CD47 blockade with conventional radiotherapy to validate this approach in humans. If successful, this innovation could revolutionize the management of metastatic cancers, transforming radiotherapy from a blunt instrument into a precision therapy tailored to counteract its own adverse systemic effects.

Dr. Weichselbaum emphasized, “Our findings open an entirely new dimension in studying radiation’s systemic influence. Radiation is no longer just a local treatment but a modulator of tumor biology throughout the body. With appropriate molecular interventions, we can harness its full therapeutic potential while neutralizing unintended tumor-promoting signals.”

This landmark discovery also highlights the broader need for integrating molecular biology, immunology, and radiation oncology to unravel the complex interdependencies that govern cancer progression and response to therapy. As metastasis remains the leading cause of cancer mortality, insights from this study will have wide-reaching implications for developing next-generation cancer therapies.

The work was supported by prominent funding sources including the National Cancer Institute and Ludwig Foundation, reflecting the critical importance and translational promise of these findings. With contributions from a multidisciplinary team spanning institutions globally, this research exemplifies the power of collaborative science to transform cancer treatment paradigms.

News Publication Date: 14-May-2025

Web References:
https://www.nature.com/articles/s41586-025-08994-0

References:
Piffkó A., Yang K., Panda A., et al. (2025). Radiation-induced amphiregulin drives tumor metastasis. Nature. https://doi.org/10.1038/s41586-025-08994-0