By Gilang Cahya 
Researchers from a consortium including the Francis Crick Institute, University College London (UCL), Gustave Roussy, and Memorial Sloan Kettering Cancer Center (MSK) have uncovered a significant link between the expansion of mutant blood cells, a hallmark of aging, and more aggressive cancer progression. This phenomenon, known as clonal hematopoiesis of indeterminate potential (CHIP), was found to be present within cancerous tumors and directly associated with poorer patient prognoses across various cancer types. The groundbreaking study, published in the prestigious New England Journal of Medicine, sheds new light on the complex interplay between aging, genetic instability, and cancer evolution, offering potential avenues for novel therapeutic interventions.
The Growing Threat of Age-Related Diseases and the Unseen Influence of CHIP
As global populations age, the prevalence of age-related diseases, including cancer and cardiovascular conditions, continues to rise. Understanding the intricate biological mechanisms that bridge age-related genetic alterations and these diseases is paramount for developing effective preventative and therapeutic strategies. Clonal hematopoiesis of indeterminate potential (CHIP) has emerged as a critical area of investigation in this regard. CHIP is characterized by the accumulation of somatic mutations in blood stem cells, a process influenced by both the natural course of aging and exposure to external environmental factors. While CHIP has been previously linked to an increased risk of cardiovascular disease and hematological malignancies, its impact on the evolution and prognosis of solid tumors remained largely unexplored until now.
The current research represents a comprehensive investigation into this understudied connection. Leveraging data from over 400 lung cancer patients enrolled in the Cancer Research UK-funded TRACERx and PEACE studies, and an additional 49,000 patients with diverse cancer types from Memorial Sloan Kettering Cancer Center, the scientists aimed to quantify the prevalence of CHIP in cancer patients and assess its prognostic value.
Unveiling the Prognostic Power of CHIP in Cancer Patients
The initial phase of the study involved meticulous analysis of blood samples from patients. By identifying the presence of specific CHIP-associated mutations in their blood, the research team was able to correlate these genetic signatures with clinical outcomes. The findings were stark: patients with CHIP mutations in their blood had a significantly shorter lifespan, irrespective of their age at diagnosis or the stage of their cancer. This initial observation underscored the pervasive influence of these age-related blood cell changes on overall cancer prognosis.
However, the researchers hypothesized that the impact might be even more profound when these mutant blood cells directly infiltrate tumor sites. To investigate this, they examined tumor tissue samples to determine if the CHIP mutations identified in the blood were also present within the cancerous growths. This phenomenon, termed tumor-infiltrating clonal hematopoiesis (TI-CH), was detected in a substantial 42% of patients with CHIP. Crucially, it was TI-CH, rather than CHIP alone, that emerged as the strong predictor of increased risk for cancer relapse and cancer-related mortality.
This critical finding was further corroborated by data from the PEACE study, which involved a postmortem investigation of metastatic sites – the areas where cancer spreads and ultimately leads to death. The analysis revealed that metastatic tumors at these advanced sites frequently harbored TI-CH mutations, reinforcing the notion that these age-related blood cell changes play an active role in cancer dissemination and lethality.
Differentiating the Impact: Not All Mutations Are Created Equal
The study then delved deeper into the cellular composition of lung tumors to understand why TI-CH specifically confers a worse prognosis. Scientists observed that patients with TI-CH exhibited an expansion of myeloid cells within their tumors. Myeloid cells are a crucial component of the tumor microenvironment. Unlike some immune cells that are programmed to detect and destroy cancer cells, myeloid cells are known to modulate inflammation and can actively promote tumor growth and spread.
Furthermore, the research identified a specific gene, TET2, as a key player. TET2 is vital for regulating blood cell production. When mutations affecting TET2 were present in blood cells, these mutant cells demonstrated a greater propensity to infiltrate tumors. Subsequent single-cell analysis of tumors from two patients with TI-CH confirmed that TET2 mutations were predominantly found within myeloid cells, but not in other types of immune cells, suggesting a selective infiltration mechanism.
To experimentally validate these findings, the team collaborated with experts in blood cancer and CHIP at the Crick, led by Dominique Bonnet. They developed organoid models, essentially miniature lung tumors grown in the lab, incorporating TET2-mutant myeloid cells. Their experiments conclusively demonstrated that these TET2-mutant myeloid cells actively remodeled the tumor microenvironment and accelerated the growth of the tumor organoids. This experimental evidence provided a direct causal link between TET2-mutant myeloid cell infiltration and enhanced tumor aggressiveness.
Broadening the Horizon: TI-CH Across Diverse Cancer Types
The researchers extended their investigation beyond lung cancer by collaborating with scientists at Memorial Sloan Kettering Cancer Center in the United States. They analyzed an extensive dataset comprising over 49,000 patients with a wide spectrum of cancer types. This large-scale validation confirmed that the presence of TI-CH was an independent predictor of shorter survival across diverse malignancies.
However, the prevalence of CHIP and TI-CH varied significantly between different cancer types. The study revealed that these age-related blood cell mutations were more commonly observed in cancers that are notoriously difficult to treat, including lung cancer, head and neck cancer, and pancreatic cancer. This observation suggests that TI-CH might contribute to the inherent resistance or aggressive nature of these particular cancers.
Future Directions and Implications for Intervention
The implications of this research are far-reaching. The identification of TI-CH as a driver of poor cancer outcomes opens up new avenues for risk stratification and personalized treatment approaches. The next critical steps for the research team involve definitively proving that CHIP directly contributes to adverse cancer outcomes and meticulously detailing the precise biological mechanisms through which CHIP functionally influences the development of aggressive cancers.
Dr. Oriol Pich, a lead researcher on the project and Postdoctoral Project Research Scientist at the Crick, emphasized the significance of the findings: "Our results demonstrate that blood cells harboring age-related mutations can infiltrate tumors and influence cancer evolution, leading to worse outcomes for patients. This is particularly important because CHIP is a natural phenomenon of aging that is prevalent in individuals with cancer."
Professor Charlie Swanton, Deputy Clinical Director at the Crick, Chief Clinician at Cancer Research UK, and Chief Investigator for TRACERx, highlighted the novelty of the work: "This is the first time we have been able to observe, at scale, the interaction of two distinct types of clonal proliferation – age-related CHIP and cancer. This provides invaluable insight into how aging itself might influence cancer risk. As we continue to unravel the critical mutations that arise during the aging process in bone marrow cells and their impact on disease, we hope to identify opportunities for intervention and potentially even the prevention of certain age-related cancers."
The study was generously supported by Cancer Research UK and the National Institute of Health and Care Research UCLH Biomedical Research Centre, along with additional funding bodies, underscoring the collaborative and well-supported nature of this critical scientific endeavor. The findings lay the groundwork for future research aimed at developing diagnostic tools to identify patients at higher risk due to TI-CH and exploring therapeutic strategies to mitigate its impact, potentially by targeting the infiltrating myeloid cells or the specific mutations they carry. This advancement marks a significant step forward in understanding the complex biology of cancer in an aging population.
