By Billy Candra 
A landmark study, published today in the prestigious New England Journal of Medicine, has unveiled a critical link between age-related genetic changes in blood cells and the progression of solid cancers, a finding poised to reshape our understanding of cancer evolution and patient prognosis. The research, a collaborative effort spanning leading institutions across the UK, France, and the US, reveals that certain mutations in blood stem cells, common with advancing age, not only infiltrate tumours but actively contribute to more aggressive disease outcomes, including increased risk of relapse and death. This discovery bridges the often-separate fields of ageing biology and oncology, underscoring the profound interplay between age-related physiological changes and the complex mechanisms driving cancer.
Unpacking Clonal Haematopoiesis of Indeterminate Potential (CHIP)
At the heart of this groundbreaking research lies Clonal Haematopoiesis of Indeterminate Potential, or CHIP. CHIP is a condition characterized by the accumulation of specific mutations in blood stem cells over time. These mutations lead to the expansion of a "clone" of blood cells derived from a single mutated stem cell, which can eventually dominate the bone marrow’s blood cell production. While CHIP is not a cancer in itself, it has long been recognized as a risk factor for various age-related disorders, notably cardiovascular disease and certain inflammatory conditions.
The prevalence of CHIP increases significantly with age. Studies indicate that approximately 10-15% of individuals over the age of 65 exhibit evidence of CHIP, a figure that can climb to 20-30% in those over 80. This demographic trend highlights its growing importance in an increasingly ageing global population. The initial understanding of CHIP primarily focused on its association with haematological malignancies, where these mutations could, in some cases, precede the development of blood cancers like myelodysplastic syndromes or acute myeloid leukaemia. However, its broader impact on solid tumour evolution remained largely uninvestigated until now.
These mutations in blood stem cells can arise from various factors, including cumulative DNA damage, environmental exposures, and chronic inflammation, all of which tend to increase with age. The most commonly affected genes in CHIP include TET2, DNMT3A, and ASXL1, all of which play crucial roles in regulating blood cell development and function. The presence of these mutations allows the mutated blood stem cells to have a survival or proliferative advantage, leading to their clonal expansion.
A Detailed Study Across Vast Patient Cohorts
The research presented in the New England Journal of Medicine represents an extensive and meticulous investigation into the relationship between CHIP and solid cancers. The study leveraged data from multiple, large-scale patient cohorts, providing robust validation for its findings. Key among these were the Cancer Research UK-funded TRACERx and PEACE studies, which focused on over 400 patients with lung cancer in the UK. Complementing these was an even larger dataset from Memorial Sloan Kettering Cancer Center (MSK) in the US, encompassing over 49,000 patients with diverse types of cancer. This multi-cohort approach allowed the researchers to not only identify specific correlations but also to validate them across different populations and cancer types, enhancing the generalizability and reliability of their conclusions.
The initial phase of the investigation involved examining blood samples from lung cancer patients to determine the presence of CHIP mutations. When these genetic findings were correlated with comprehensive clinical data, a concerning pattern emerged: patients harbouring CHIP mutations in their blood exhibited a statistically significant shorter overall survival. Crucially, this association remained independent of other well-established prognostic factors, such as the patient’s age at diagnosis or the stage of their cancer. This early observation suggested that CHIP was not merely a bystander phenomenon but an active participant in the disease trajectory.
From CHIP to Tumour Infiltrating Clonal Haematopoiesis (TI-CH)
While the initial link between CHIP and poorer outcomes was compelling, the researchers delved deeper to understand the underlying mechanism. A critical distinction was made between CHIP, the presence of these mutations in circulating blood, and a newly defined phenomenon: Tumour Infiltrating Clonal Haematopoiesis (TI-CH). The team meticulously analyzed tumour tissue samples from patients with CHIP to ascertain whether these specific mutant blood cells had infiltrated the solid tumour microenvironment.
Remarkably, they discovered that TI-CH was present in 42% of lung cancer patients who had CHIP. This finding was pivotal. Further analysis revealed that it was TI-CH, rather than CHIP alone, that was strongly associated with a greater risk of cancer relapse and, ultimately, cancer-related mortality. This suggested that the physical presence of these mutant blood cells within the tumour was a key determinant of its aggressive behaviour.
This crucial finding was independently corroborated by samples from the PEACE study, a unique post-mortem investigation designed to map the spread of cancer to metastatic sites – the primary cause of cancer death. The team found that metastatic tumours at these secondary sites frequently contained TI-CH mutations, providing compelling evidence that these infiltrating cells play a role in the most lethal aspects of cancer progression. The implication is profound: age-related mutant blood cells are not just circulating innocuously but are actively participating in the tumour’s destructive journey.
The Myeloid Cell Connection and the Role of TET2 Mutations
To unravel how TI-CH exerted its detrimental effects, the scientists turned their attention to the cellular composition of the lung tumours. They observed that patients with TI-CH exhibited an expanded presence of myeloid cells within their tumours. Myeloid cells are a type of immune cell that form a significant component of the tumour microenvironment (TME). Unlike some immune cells, such as certain T-cells, which are primed to recognize and eliminate cancer cells, myeloid cells have a more complex and often paradoxical role in cancer. They are known to regulate inflammation, and critically, many subsets of myeloid cells, such as myeloid-derived suppressor cells (MDSCs) and tumour-associated macrophages (TAMs), have been shown to promote tumour progression, angiogenesis (new blood vessel formation), and metastasis, effectively shielding cancer cells from immune attack and supporting their growth.
Further investigation pinpointed a specific genetic culprit: mutations in the TET2 gene. TET2 is a vital regulator of blood cell production and function, involved in epigenetic modifications that control gene expression. Across thousands of individuals, the researchers discovered that when mutations affected TET2, these mutant blood cells were significantly more likely to infiltrate the tumour. To confirm this at a granular level, hundreds of single cells from the tumours of two patients with TI-CH were analyzed. This single-cell resolution analysis confirmed that TET2 mutations were predominantly found within myeloid cells, but notably absent in other immune cell types present in the tumour, further solidifying the link between TET2-mutated myeloid cells and TI-CH.
To functionally validate these observations, the research team collaborated with experts in blood cancer and CHIP at the Crick Institute, specifically in the laboratory led by Dominique Bonnet. Together, they conducted experimental studies using organoids – miniature lung tumours grown in a laboratory setting. By co-culturing these organoids with TET2 mutant myeloid cells, they demonstrated a direct causal link. The TET2 mutant myeloid cells actively remodelled the tumour microenvironment, creating a more permissive and growth-promoting niche, and significantly accelerated the growth of the tumour organoids. This experimental evidence provided compelling proof that TET2-mutated myeloid cells are not merely markers of aggressive disease but active contributors to its progression.
Broader Validation Across Cancer Types and Future Horizons
The robust findings from the lung cancer cohorts were then validated using the extensive dataset of over 49,000 patients with various cancer types from Memorial Sloan Kettering Cancer Center. This large-scale analysis confirmed that, overall, the presence of TI-CH served as an independent predictor of shorter survival across a spectrum of malignancies. However, the prevalence of CHIP and TI-CH varied significantly between different cancer types. Researchers observed that these mutations were more common in cancers notoriously difficult to treat, such as lung cancer, head and neck cancer, and pancreatic cancer. This observation raises a crucial hypothesis: could the presence of TI-CH contribute to the inherent aggressiveness and poor prognosis associated with these particular cancer types?
This comprehensive study lays the groundwork for several critical next steps. The immediate priority for researchers will be to definitively confirm that CHIP directly contributes to adverse cancer outcomes through the mechanisms observed, moving beyond association to establish causality with even greater certainty. Following this, the precise molecular and cellular mechanisms by which CHIP, particularly through TET2-mutated myeloid cells, functionally implicates itself in the development and progression of aggressive cancers will need to be fully detailed. This could involve exploring specific cytokine pathways, immune checkpoints, or metabolic interactions within the tumour microenvironment.
Expert perspectives underscore the significance of these findings. Oriol Pich, a Postdoctoral Project Research Scientist in the Crick’s Cancer Evolution and Genome Instability Laboratory and a lead author of the study, emphasized, "Our results show that blood cells carrying age-related mutations can infiltrate tumours and impact cancer evolution, leading to worse outcomes for patients. This is important because CHIP is a natural phenomenon of ageing that is common in patients with cancer." This highlights the broad clinical relevance, given the increasing age of cancer patients globally.
Charlie Swanton, Deputy Clinical Director at the Crick, Chief Clinician at Cancer Research UK, and Chief Investigator for TRACERx, commented on the broader implications: "This is the first time that we’ve been able to see at scale, the interaction of two different types of ‘clonal proliferations,’ age-related CHIP and cancer, providing insight into how ageing might impact cancer risk." He expressed optimism about future interventions: "As we start to piece together the picture of the most important mutations which evolve during the ageing process in cells from the bone marrow, and the impact they have in disease, we hope we can start to identify opportunities for intervention and maybe even prevention of some age-related cancers."
The potential clinical ramifications of this research are substantial. Identifying CHIP and TI-CH could lead to novel prognostic biomarkers, allowing clinicians to stratify patients more accurately and tailor treatment strategies for those at higher risk. For instance, patients with TI-CH might benefit from more aggressive initial therapies or targeted interventions aimed at modulating the pro-tumourigenic activity of myeloid cells. Furthermore, understanding the precise mechanisms could open avenues for therapeutic intervention, potentially through drugs that target the specific pathways activated by TET2 mutations or through immunotherapies designed to reprogramme the tumour-infiltrating myeloid cells.
Given the demographic shift towards an ageing global population, the interplay between ageing and age-related diseases like cancer is becoming increasingly critical. This study offers a crucial piece of the puzzle, suggesting that the natural process of ageing, through the accumulation of CHIP mutations, can directly influence the aggressiveness and prognosis of solid cancers. This discovery paves the way for a more integrated approach to cancer care, one that considers not just the genetics of the tumour itself but also the age-related biological landscape of the patient, ultimately fostering the development of preventative therapies and more personalized treatment strategies for a growing proportion of the population.
This monumental work was supported by significant contributions from Cancer Research UK and the National Institute of Health and Care Research UCLH Biomedical Research Centre, alongside additional funders, underscoring the collaborative and well-resourced effort required for such impactful scientific breakthroughs.
