Medical Guidelines Lag Behind Evidence: The Growing Significance of Clonal Hematopoiesis

Cardiology professional organizations recently revised their guidelines to incorporate lipoprotein(a) (Lp(a)) and Apolipoprotein B (ApoB), aligning with evidence-based lipid panels published eight years prior. This delay has raised concerns that numerous individuals at high risk for atherosclerosis and cardiovascular events may have been overlooked due to outdated recommendations.

This underscores a broader challenge in medicine: the lag between groundbreaking research and its adoption into routine clinical practice. A similar trajectory is now unfolding for Clonal Hematopoiesis of Indeterminate Potential (CHIP), a condition increasingly recognized for its widespread implications for health.

Understanding Clonal Hematopoiesis of Indeterminate Potential (CHIP)

CHIP is defined by an acquired (somatic) mutation of a blood stem cell, granting it a selective advantage for clonal expansion. The abnormality is specifically identified by a clone size of 2% or greater of blood cells, or a variant allele frequency (VAF) ≥ 2% of a white blood cell driver mutation.

The prevalence of CHIP significantly increases with age:

• Approximately 2% of individuals aged 50-69
• 10% aged 70-79
• 20% aged 80-89
• Over 39% aged 90+

The most common mutations linked to CHIP include:

• DNMT3A (around 48%)
• TET2 (about 22%)
• ASXL1 (11%)
• Other genes like JAK2, TP53, and SF3B1 (19%)

Notably, the three most prevalent mutations occur in epigenetic genes, highlighting their role in regulating gene expression.

CHIP's Association with Disease

The presence of CHIP is associated with a wide array of diseases, especially cardiovascular, cancer, and inflammatory conditions, with risk escalating alongside higher CHIP frequency.

The American Heart Association has issued a scientific statement recognizing CHIP as a potential driver of cardiovascular disease. Beyond advanced age, other risk factors contribute to CHIP development. CHIP with a VAF ≥ 2% is linked to elevated inflammation and immune dysfunction—a state referred to as "inflammaging" and "immunosenescence," particularly in the context of advanced age. It also correlates with multiple cardiovascular diseases and blood cancers.

The cardiovascular disease hazard ratio for CHIP is 1.8, surpassing traditional risk factors such as smoking, hypertension, and total cholesterol >200 mg/dl (all at 1.4).

A new CHIP risk score has been proposed to further stratify risk levels. While only 0.5% to 1.0% of individuals with CHIP > 10% develop a blood cancer each year, dysfunction of the immune system and a chronic pro-inflammatory state are detectable even without overt disease. In patients with advanced solid cancers, over 25% exhibit CHIP, a rate significantly higher than age-matched healthy controls.

Recent Research Findings

Recent studies have shed light on both disease mechanisms and potential therapeutic avenues related to CHIP.

Disease-Related Discoveries

• Cancer Immunotherapy: TET2 mutations in CHIP have been associated with an improved response to checkpoint therapy for non-small cell lung cancer and colorectal cancer. The mechanism involves circulating CHIPs penetrating the tumor microenvironment, where TET2 mutant clones facilitate an increased interferon and T-cell response.
• Aortic Aneurysms: In a separate study, TET2 mutant CHIP was linked to accelerated aortic aneurysm growth due to a pro-inflammatory macrophage effect. This highlights the complex, sometimes paradoxical, roles of specific CHIP mutations.
• Protective Gene Variant: An important discovery involves a gene variant on chromosome 17, identified in three large cohorts. This variant is linked to a reduction of multiple CHIP subtypes (driver mutations) and blood cancers. The finding is related to an RNA network and specifically the down-regulation of the RNA binding protein MSI-2, suggesting a potential new intervention to suppress CHIP and its adverse health outcomes.

Treatment-Related Progress

• Low-Dose Colchicine: This anti-inflammatory drug consistently reduced CHIP in a randomized placebo-controlled trial with longitudinal sampling. Colchicine has previously been studied in atherosclerotic murine models and patient cohorts with TET2 mutations to reduce plaque and heart attacks, respectively. It is noted for being inexpensive, generic, and well-tolerated.
• Other Potential Interventions: Beyond colchicine (an NLRP3 inflammasome blocker), an IL-1β–neutralizing antibody reduced events in participants with TET2 in a randomized trial. Other candidate interventions include:
  • Metformin (against DNMT3A)
  • Vitamin C (against TET2)
  • Inhibitors to other interleukins such as IL-6
  • Other inflammasome blockers (e.g., selnoflast, currently in clinical trials for CHIP)
  • GLP-1 drugs, known for their anti-inflammatory action, have also been suggested as potential anti-CHIP interventions.

Implications and Future Directions

The growing body of data on CHIP elucidates its links to numerous diseases, including cardiovascular, cancer, thromboembolic (clotting), and liver conditions. It's clear that different driver mutations carry varying risks, and the same CHIP mutations, such as TET2, can sometimes have both detrimental (e.g., aneurysm growth) and beneficial (e.g., improved solid tumor immunotherapy response) effects. JAK2, an unusual CHIP subtype (0.5% to 4% of driver mutations), is specifically associated with clotting complications like pulmonary embolism. The causal relationship between CHIP and adverse outcomes is strongly supported by new data from multiple parallel human and animal studies.

Barriers to Widespread Adoption

Despite accumulating evidence and promising therapeutic candidates, routine CHIP assays for older individuals are not yet standard practice. Reasons cited include:

• The high cost of accurate assays (e.g., $950 for deep sequencing panels)
• The potential for inducing anxiety with high-risk results in patients.

Prioritizing the development of precise, low-cost CHIP assays is crucial, alongside dedicated clinical trials for drugs that improve outcomes.

A Call for Action and Future Guidelines

Currently, a limited number of academic centers, including the University of Chicago, Cleveland Clinic, and Yale Medicine (which has a hybrid cardio-oncology CHIP clinic), have established dedicated CHIP clinics. Experts advocate for making CHIP assessment more widely available and affordable for select individuals, such as those aged 70 and above. The information provided by CHIP is considered more specific than general inflammation markers like high-sensitivity C-reactive protein.

There is a growing call to rename the acronym to "Clonal Hematopoiesis of Important Potential," removing the "indeterminate" qualifier, to better reflect its significant clinical implications. It is anticipated that professional societies in cardiology, hematology, and oncology will eventually incorporate CHIP diagnosis and treatment utility into new guidelines, similar to the recent adoption of Lp(a) and ApoB in lipid management.