How chronic inflammation builds - and sometimes blocks - cancer

Rudolf Virchow noticed the connection in the 1860s: tumor tissue was dense with immune cells, suggesting inflammation and cancer were entangled. The past 160 years have confirmed his intuition while adding staggering complexity. Chronic inflammation now accounts for roughly 20% of all cancers worldwide, linked to infections, autoimmune conditions, and environmental exposures like tobacco smoke. But the relationship cuts both ways. The same immune signals that feed tumors can, under different conditions, destroy them.

A review published in the Journal of Exploratory Research in Pharmacology synthesizes current knowledge across this axis - from molecular mechanisms through clinical trials - and examines where precision strategies are beginning to exploit this complexity therapeutically.

The core molecular machinery

Two transcription factors dominate the story: NF-kB and STAT3. Both activate in response to inflammatory signals and both promote cell survival, angiogenesis, and immune suppression within tumors. NF-kB responds to bacteria, cytokines, and tissue damage; STAT3 is activated downstream of interleukin-6 (IL-6). Together they create a molecular environment where cancer cells proliferate and evade immune recognition.

Supporting them is a set of immune cells that tumors co-opt. Tumor-associated macrophages polarized to the M2 phenotype suppress anti-tumor immunity and promote tissue remodeling that facilitates invasion. Myeloid-derived suppressor cells (MDSCs) block T-cell activation. Regulatory T cells (Tregs) maintain immune tolerance within the tumor microenvironment. Single-cell analyses now reveal substantial heterogeneity within each of these populations, suggesting that broad targeting strategies miss important subsets.

The COX-2/PGE2 axis drives both proliferation and MDSC recruitment - which is why aspirin, a COX inhibitor, shows epidemiological associations with reduced colorectal cancer risk. The NLRP3 inflammasome activates IL-1 beta and IL-18, cytokines that perpetuate local inflammation and push cells toward proliferative states.

How this plays out by cancer type

The review distinguishes mechanisms by tumor type. In colorectal cancer, gut dysbiosis activates NF-kB and STAT3, and NLRP3 activity correlates with poor prognosis. In lung cancer, tobacco smoke and air pollution trigger COX-2/PGE2 and IL-6/STAT3 pathways; KRAS mutations amplify immunosuppression. In breast cancer, obesity-associated inflammation drives MDSC and Treg accumulation, and C-reactive protein (CRP) predicts response to neoadjuvant therapy.

These distinctions are clinically relevant. A treatment strategy targeting IL-6 may be appropriate for one tumor context and counterproductive in another. Patients with elevated neutrophil-to-lymphocyte ratio (NLR) respond differently to immunotherapy than those without - the inflammatory state is itself a predictive variable.

Immunotherapy and inflammation: a complicated partnership

Immune checkpoint inhibitors - drugs blocking PD-1, PD-L1, or CTLA-4 to restore T-cell activity - produce durable responses in 20 to 40% of eligible patients depending on tumor type. Elevated IL-6 predicts resistance, meaning inflammatory tumor environments can actively undermine these drugs. LAG-3 blockade via relatlimab received regulatory approval in 2024, adding a new target to the checkpoint inhibitor arsenal.

Clinical trials are now testing whether combining checkpoint inhibitors with anti-inflammatory agents improves outcomes. Tocilizumab and siltuximab target IL-6 or its receptor; infliximab targets TNF-alpha. 2025 trials combining IL-6 blockade with checkpoint inhibitors in pancreatic cancer aim to test whether clearing inflammatory signals allows immune cells to function more effectively. These results will materially shape treatment guidelines when they report.

CAR-T cells remain effective in hematologic malignancies but face barriers in solid tumors - the inflammatory tumor microenvironment exhausts engineered cells and impairs their function. CRISPR-edited CAR-T cells with modified exhaustion genes show improved persistence in preclinical models. Translation to routine clinical use remains years away.

Biomarkers: who benefits and who doesn't

Established inflammatory markers - CRP, IL-6, NLR, and the pan-immune-inflammation value (PIV) - correlate with prognosis and checkpoint inhibitor response but are imprecise. PD-L1 expression, tumor mutational burden (TMB), and microsatellite instability (MSI) predict checkpoint inhibitor response more specifically. Microbiome composition has emerged as an additional variable: Bifidobacterium and Akkermansia species correlate with better checkpoint inhibitor responses, and fecal microbiota transplantation studies are now testing whether microbiome manipulation can convert non-responders.

AI-driven models integrating imaging data, genomics, and clinical variables promise more precise patient stratification. A 2024 Stanford model combining imaging and text data demonstrated this approach, though prospective validation is needed before clinical adoption.

Where the field stands honestly

Much of the preclinical work uses mouse models that incompletely recapitulate human tumor immunology. Combination strategies that appear synergistic in mice have often disappointed in clinical trials. The toxicity of combining immunotherapy with anti-inflammatory drugs needs careful characterization - suppressing inflammation too broadly risks undermining anti-tumor immune function at the same time.

The promise is real: inflammation drives cancer and can be targeted. The complexity is equally real: which pathway, which patients, and which combinations at what sequence are questions that current evidence only partially answers.