Myokine Signaling Emerges as a Central Variable in Rectal Cancer ICI Toxicity
Rectal cancer presents a biologically uneven target for immune checkpoint inhibitors, and the same immune activation that can suppress a mismatch repair-deficient or MSI-H tumor can also injure the bowel that surrounds it. In this setting, immune checkpoint inhibitor-associated colorectal injury is not a minor adverse event. It can begin as diarrhea, progress to mucosal ulceration, and in severe cases advance to perforation. The clinical problem is especially sharp in rectal cancer, where local anatomy, tumor heterogeneity, and the intestinal immune ecosystem converge in a confined space.
The review places the gut-muscle axis at the center of this toxicity. Skeletal muscle is no longer treated as a passive metabolic reservoir; it is an endocrine organ that releases myokines with direct immunologic consequences. Among the mediators discussed, IL-6, IL-15, and irisin form a biologically plausible network linking muscle status to mucosal integrity, inflammatory tone, and treatment tolerance. In practical terms, muscle wasting is not simply a background finding in advanced cancer. It may feed forward into intestinal damage while intestinal injury further accelerates weakness and loss of reserve.
The implications are immediate at the bedside. A patient with falling lean mass may be carrying a higher inflammatory burden before any endoscopic lesion is visible.
CD8+ Cytotoxicity, Cytokines, and the Mucosal Breakdown Sequence
At the core of ICI-related injury sits an immune system that is working as intended for the tumor and misfiring against the gut. The review describes CD8+ T cell-mediated epithelial cytotoxicity as one of the main drivers of mucosal damage. Once epithelial cells are attacked, the intestinal barrier weakens, allowing inflammatory mediators and microbial products to amplify local injury. The result is not a single-pathway event but a layered cascade involving cytokine release, epithelial loss, vascular compromise, and repair failure.
Inflammatory cytokines deepen the injury. Excessive immune signaling keeps the bowel in a persistent activated state, and the mucosa loses its ability to restore architectural integrity between inflammatory hits. In parallel, gut dysbiosis and endotoxin translocation worsen the inflammatory load by feeding microbial signals into an already primed immune compartment. The resulting environment can become self-sustaining, with ongoing diarrhea and ulceration reinforcing dehydration, malnutrition, and further immune dysregulation.
Microvascular hypoperfusion adds another layer of harm. When blood flow falls, oxygen delivery drops and epithelial repair slows. Lactic acid accumulation then marks a tissue environment that is metabolically stressed and less capable of efficient recovery. Fibrosis completes the cycle by replacing flexible, functional tissue with stiff extracellular matrix, making the mucosa more vulnerable to repeated injury and less responsive to healing signals.
IL-15 and Irisin as Mucosal Protectors, IL-6 as a Double-Edged Signal
The most clinically interesting part of the review is the asymmetry among myokines. IL-15 and irisin are framed as protective mediators that help preserve intestinal mucosa by restraining immunosuppressive cells. In a tumor setting, reducing excessive immune suppression can be useful, but in the bowel it may also help maintain a more balanced tissue defense without collapsing the epithelial barrier. These signals suggest that muscle biology may influence whether the intestine tolerates the immune pressure generated by checkpoint blockade.
IL-6 occupies a far less reassuring position. Muscle-derived IL-6 can intensify intestinal inflammation when present in excess, turning a normally adaptive stress signal into a contributor to pathology. This creates a clinically important tension: not all exercise-associated or muscle-associated signaling is uniformly protective. The net effect depends on timing, magnitude, and the inflammatory state of the host. In a patient with rectal cancer receiving immunotherapy, sarcopenia may therefore be more than a prognostic marker. It may represent a biologic amplifier of bowel toxicity.
This framing also helps explain why nutritional decline and intestinal injury so often travel together. Reduced muscle mass can shift the myokine balance toward a less protective profile, while ongoing colitis or proctitis can reduce intake, worsen catabolism, and deepen weakness. The circle closes quickly.
Imaging, Radiomics, and Artificial Intelligence as Tools for Toxicity Mapping
The review also moves beyond biology into measurement. Multimodal imaging combined with radiomics and artificial intelligence offers a way to quantify mucosal, vascular, and fibrotic changes that are difficult to capture with routine clinical assessment alone. In a disease process where inflammation, perfusion, and remodeling all evolve at different speeds, imaging-based phenotyping could help separate active injury from later repair or scar formation.
That matters because treatment intensity should not depend only on symptom severity. A patient with worsening vascular compromise or increasing fibrosis may need a different response than one with reversible inflammatory diarrhea. Quantitative imaging could help clinicians identify which component of the injury process is dominant at a given time. It could also support earlier intervention, before edema and ulceration progress to deeper tissue disruption.
Stepwise Immunosuppression and Supportive Repair Strategies
The review outlines a stratified management approach that combines stepwise immunosuppression with microbiota reconstruction, metabolic support, and muscle-targeted exercise or nutrition. Each element addresses a different part of the injury loop. Immunosuppression lowers the immediate inflammatory assault. Microbiota reconstruction may reduce endotoxin translocation and rebalance the intestinal environment. Metabolic support can offset catabolic loss, while exercise and nutrition aim to restore the muscle compartment that helps regulate myokines in the first place.
This is a more integrated view of toxicity than the usual binary model of “hold treatment and treat colitis.” In rectal cancer, bowel injury and sarcopenia may be biologically entangled, so recovery likely requires more than suppression of inflammation alone. If muscle loss continues unchecked, the patient may remain stuck in a state of vulnerability even after acute symptoms ease. Repair then becomes incomplete, and the bowel remains easy to injure again.
The review’s central message is straightforward: optimizing checkpoint inhibitor efficacy in rectal cancer requires more than identifying the right tumor genotype. It also requires attention to the host tissue systems that determine whether antitumor immunity stays confined to the tumor or spills into the bowel wall. The myokine network offers one of the clearest mechanistic bridges between those two outcomes, although the clinical thresholds for intervention, the best biomarkers for risk, and the timing of muscle-directed therapy remain undefined in routine practice.