By Gilang Cahya 
Researchers from a global consortium, including the Francis Crick Institute, University College London (UCL), Gustave Roussy, and Memorial Sloan Kettering Cancer Center (MSK), have unveiled a significant link between age-related genetic changes in blood cells and the progression of cancerous tumors. Their groundbreaking study, published in the prestigious New England Journal of Medicine, reveals that the expansion of mutant blood cells, a phenomenon known as clonal hematopoiesis of indeterminate potential (CHIP), can infiltrate solid tumors and is directly associated with poorer prognoses for cancer patients. This discovery offers crucial insights into the complex interplay between aging, genetic instability, and the development of age-related diseases, particularly cancer, which disproportionately affects an aging global population.
The Silent Intruder: Unpacking Clonal Hematopoiesis
Clonal hematopoiesis, specifically CHIP, arises from the accumulation of acquired mutations in hematopoietic stem cells – the progenitors of all blood cells. This process is influenced by both the natural aging of the body and environmental factors, such as exposure to toxins or radiation. While CHIP has previously been recognized as a risk factor for cardiovascular disease and other age-related conditions, its direct impact on the evolution and behavior of solid cancers remained largely unexplored until this extensive investigation.
The study, a collaborative effort drawing on data from the Cancer Research UK-funded TRACERx and PEACE studies, analyzed blood samples from over 400 lung cancer patients. This was further augmented by an immense dataset of 49,000 patients with various cancer types from MSK, providing a robust and diverse patient cohort.
A Grim Association: CHIP and Cancer Prognosis
The initial phase of the research involved examining blood samples to identify the presence of CHIP mutations. When this genetic information was cross-referenced with clinical outcomes, a stark correlation emerged: patients with CHIP mutations in their blood lived for a significantly shorter period, irrespective of their age at diagnosis or the stage of their cancer. This finding alone underscored the potential detrimental influence of these age-related cellular changes on cancer survival.
However, the researchers sought to understand the mechanism behind this association more deeply. They proceeded to investigate whether these CHIP mutations, originating in the blood, were also present within the patients’ solid tumors. This infiltration of mutant blood cells into the tumor microenvironment was termed "tumour infiltrating clonal haematopoiesis" (TI-CH). The study found that TI-CH was present in a substantial 42% of patients with CHIP. Crucially, it was this TI-CH, rather than CHIP in isolation, that demonstrated a significantly higher risk of cancer relapse and cancer-related mortality.
Metastasis and the Shadow of TI-CH
The grim implications of TI-CH were further corroborated by data from the PEACE study. This postmortem investigation, which meticulously examines areas where cancer has spread – the primary driver of cancer death – provided compelling evidence. Metastatic tumors at these widespread sites frequently contained TI-CH mutations. This suggests that the infiltration of mutant blood cells into tumors is not confined to the primary site but actively participates in the aggressive spread of cancer throughout the body.
Not All Mutations Are Equal: The Role of Myeloid Cells and TET2
Delving deeper into the relationship between TI-CH and poor patient outcomes, the scientists meticulously analyzed the cellular composition of lung tumors. They observed that in patients with TI-CH, there was a marked expansion of myeloid cells, a specific type of immune cell. Myeloid cells play a critical role in the tumor microenvironment. Unlike some immune cells that are programmed to attack cancer, myeloid cells are known to modulate inflammation and can, in certain contexts, promote tumor growth and metastasis.
The research also highlighted the significance of specific gene mutations. Mutations affecting the TET2 gene, a crucial regulator of blood cell production, were found to be particularly prevalent. The study indicated that TET2 mutant blood cells were more likely to infiltrate tumors. Further single-cell analysis of tumor samples from patients with TI-CH confirmed that TET2 mutations were predominantly found within myeloid cells, not other immune cell populations.
To experimentally validate these findings, the research team collaborated with experts in blood cancer and CHIP at the Crick Institute. They successfully cultured organoids, essentially miniature tumors, incorporating TET2 mutant myeloid cells. Their experiments demonstrated that these mutant myeloid cells actively remodeled the tumor microenvironment and accelerated the growth of the tumor organoids. This experimental evidence provides a clear mechanistic link between TET2 mutations in myeloid cells and enhanced tumor aggressiveness.
A Broad Spectrum: TI-CH Beyond Lung Cancer
The global nature of this research was further solidified by its collaboration with researchers at Memorial Sloan Kettering Cancer Center in the United States. This partnership enabled the validation of the study’s findings across a much larger and more diverse dataset, encompassing over 49,000 patients with a wide array of cancer types. The results were consistent: the presence of TI-CH independently predicted shorter survival across different cancers.
However, the prevalence of CHIP and TI-CH varied significantly depending on the cancer type. The researchers observed a higher incidence of these mutations in cancers that are notoriously difficult to treat, including lung cancer, head and neck cancer, and pancreatic cancer. This suggests that the interplay between aging-related blood cell mutations and cancer may be a more significant factor in the progression of aggressive and treatment-resistant malignancies.
Future Directions and Implications
The immediate next steps for this research program involve confirming that CHIP directly contributes to adverse cancer outcomes and elucidating the precise molecular mechanisms by which CHIP functionally influences the development of aggressive cancers. This deeper understanding is paramount for developing targeted interventions.
Oriol Pich, a Postdoctoral Project Research Scientist at the Crick and one of the lead authors, emphasized the significance of these findings: "Our results show that blood cells carrying age-related mutations can infiltrate tumors and impact cancer evolution, leading to worse outcomes for patients. This is important because CHIP is a natural phenomenon of aging that is common in patients with cancer."
Charlie Swanton, Deputy Clinical Director at the Crick and Chief Clinician at Cancer Research UK, highlighted the novelty of this research: "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. 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 implications of this research are far-reaching. As the global population ages, the incidence of both CHIP and cancer is expected to rise. Understanding how these two age-related phenomena intersect could revolutionize cancer prevention and treatment strategies. Identifying patients with CHIP could potentially flag individuals at higher risk for aggressive cancer progression, allowing for more intensive monitoring or personalized therapeutic approaches. Furthermore, the findings open avenues for developing therapies that specifically target the detrimental effects of mutant myeloid cells within the tumor microenvironment, potentially offering new hope for patients with difficult-to-treat cancers.
This significant research was made possible through the generous support of Cancer Research UK and the National Institute of Health and Care Research UCLH Biomedical Research Centre, along with additional funding bodies. The collaborative spirit and robust scientific inquiry demonstrated by these institutions have provided a critical leap forward in our understanding of cancer biology and the aging process.