A New Player in Cancer Development: Tumor-Infiltrating Clonal Hematopoiesis (TI-CH)

Cancer research continually brings surprising discoveries. One is the concept of "tumor-infiltrating clonal hematopoiesis (Tumor-Infiltrating Clonal Hematopoiesis - TI-CH)."

Hematopoiesisis the process by which stem cells in the bone marrow develop into blood cells: Red blood cells, white blood cells, and platelets.

Clonal hematopoiesis occurs when a genetic mutation causes a particular stem cell lineage to expand abnormally and become dominant during this process.

On April 24, 2025, NEJM published a comprehensive article that brought TI-CH to widespread scientific attention, highlighting its importance for cancer progression and treatment. What exactly is TI-CH, and why does it matter?

What Is TI-CH?

TI-CH involves tumor infiltration by cells associated with an age-related condition called clonal hematopoiesis of indeterminate potential (Clonal Hematopoiesis of Indeterminate Potential - CHIP). In CHIP, mutations cause some bone marrow-derived blood cells to expand abnormally with age. This is not cancer in itself, but it increases the risk of chronic conditions such as cardiovascular disease and cancer. Infiltration of cancer tissue by these mutated blood cells is called TI-CH.

In other words, blood cells arising from age-related mutations migrate into cancer tissue and establish themselves within tumors. This changes tumor behavior and its relationship with the immune system.

The illustration aboveschematically depicts the role of age-related clonal hematopoiesis in tumor development, particularly cells carrying mutations in genes such as TET2. The blue and pink cells at the bottom represent bone marrow-derived hematopoietic cells that, through mutations over time, undergo clonal expansion . Some of these mutant cells, particularly monocytes, travel through the circulation to lung tumor tissue (Clonal hematopoiesis–mutant monocyte migration). These tumor-infiltrating clonal cells (TI-CH) enter the tumor microenvironment , disrupt the balance of immune cells, increase inflammation, and ultimately contribute to tumor progression . This process may lead to more aggressive cancer and treatment resistance. The illustration clearly shows how TI-CH has become a critical player in cancer biology.

How Common Is TI-CH?

Recent large-scale research has shown that TI-CH is relatively common:

• If CHIP is present in 42% of patients with lung cancer (non-small cell lung cancer, NSCLC), nearly half of these patients have TI-CH.

• Across all solid tumors, TI-CH was detected in 26% of patients with CHIP.

These figures show that TI-CH is far from rare among cancer patients.

Clinical Significance of TI-CH: Risk of Death and Recurrence

One of the most striking findings was that TI-CH directly affected survival and the risk of disease recurrence:

• In patients with lung cancer, TI-CH increases the risk of death or cancer recurrence by approximately 80%.

• Across solid tumors overall, TI-CH increases the risk of death by 17% compared with patients who have CHIP without TI-CH.

These findings suggest that TI-CH could be an important marker in cancer treatment and follow-up.

How Were CHIP and TI-CH Detected?

1. How Was CHIP Identified?

CHIP (clonal hematopoiesis of indeterminate potential) was identified in DNA from blood or normal tissue samples by examining known CHIP-associated genes, such as TET2, DNMT3A, and ASXL1, using targeted sequencing . In these analyses:

• Mutations with a variant allele frequency (VAF) >2% were classified as CHIP.

• VAF indicates the proportion of mutated cells; for example, a 10% VAF may mean that one in every 10 cells carries the mutation.

Data sources:

• TRACERx study (patients with early-stage non-small cell lung cancer, n=421)

• MSK-IMPACT cohort (49,351 patients with solid tumors)

2. How Was TI-CH Defined?

TI-CH was identified through bioinformatic analysis showing that mutations in tumor tissue originated not in the tumor itself but in CHIP-derived hematopoietic cells . The process works as follows:

• DNA from both tumor tissue and matched blood or normal tissue is sequenced.

• If a mutation in the tumor is also found with the same genetic profile in the blood sample, it is considered hematopoietic in origin.

• If this CHIP-derived mutation also has a high VAF in tumor tissue, TI-CH is considered present.

In brief: Some mutations in tumor tissue actually belong to mutated blood cells infiltrating the tumor microenvironment rather than to the tumor itself. This is TI-CH.

TET2 Mutation: A Leading Player in TI-CH

TET2 was the mutation most strongly linked to TI-CH. TET2 mutation promotes immune-cell migration to the tumor and enriches the tumor microenvironment with immune cells. This accelerates tumor growth and development.

Mouse experiments clearly showed that blood cells with TET2 mutations accelerated tumor organoid growth. These findings indicate that TI-CH directly shapes tumor biology and the immune system.

Why Does TI-CH Matter, and What Comes Next?

The discovery of TI-CH could transform cancer treatment and follow-up. A better understanding may:

• Help identify patients who need more aggressive treatment.

• Explain how tumors evade the immune system.

• Open the door to new targeted treatments.

Detailed investigation of TI-CH could make personalized cancer treatment more effective.

Conclusion

Tumor-infiltrating clonal hematopoiesis (TI-CH) occurs when age-related mutated blood cells enter cancer tissue and accelerate cancer progression. With important implications for patients with lung cancer and other solid tumors, TI-CH has become a major focus of cancer research. Future studies will clarify its clinical applications and role in combating cancer.

Every new insight in the fight against cancer brings new hope. Understanding TI-CH could open an entirely new chapter in cancer treatment.