How Do Findings Compare With Those of the UK Biobank Study?
CHIP was associated with a 30% increased risk for breast cancer (hazard ratio [HR], 1.30; 95% CI, 1.03-1.64; P = .02), strengthening the borderline association reported by the UK Biobank study.
In contrast with the UK Biobank study, CHIP was not associated with lung cancer risk, although this may have been caused by fewer cases of lung cancer and a lack of male patients, Dr. Desai suggested.
“The discrepancy between the studies lies in the risk of lung cancer, although the point estimate in the current study suggested a positive association,” wrote Dr. Takahashi and Ms. Shah.
As in the UK Biobank study, CHIP was not associated with increased risk of developing colorectal cancer.
Mortality analysis, however, which was not conducted in the UK Biobank study, offered a new insight: Patients with existing colorectal cancer and CHIP had a significantly higher mortality risk than those without CHIP. Before stage adjustment, risk for mortality among those with colorectal cancer and CHIP was fourfold higher than those without CHIP (HR, 3.99; 95% CI, 2.41-6.62; P < .001). After stage adjustment, CHIP was still associated with a twofold higher mortality risk (HR, 2.50; 95% CI, 1.32-4.72; P = .004).
The investigators’ first mCA analyses, which employed a cell fraction cutoff greater than 3%, were unfruitful. But raising the cell fraction threshold to 5% in an exploratory analysis showed that autosomal mCA was associated with a 39% increased risk for breast cancer (HR, 1.39; 95% CI, 1.06-1.83; P = .01). No such associations were found between mCA and colorectal or lung cancer, regardless of cell fraction threshold.
The original 3% cell fraction threshold was selected on the basis of previous studies reporting a link between mCA and hematologic malignancies at this cutoff, Dr. Desai said.
She and her colleagues said a higher 5% cutoff might be needed, as they suspected that the link between mCA and solid tumors may not be causal, requiring a higher mutation rate.
Why Do Results Differ Between These Types of Studies?
Dr. Takahashi and Ms. Shah suggested that one possible limitation of the new study, and an obstacle to comparing results with the UK Biobank study and others like it, goes beyond population heterogeneity; incongruent findings could also be explained by differences in whole genome sequencing (WGS) technique.
“Although WGS allows sensitive detection of mCA through broad genomic coverage, it is less effective at detecting CHIP with low variant allele frequency (VAF) due to its relatively shallow depth (30x),” they wrote. “Consequently, the prevalence of mCA (18.8%) was much higher than that of CHIP (8.3%) in this cohort, contrasting with other studies using deeper sequencing.” As a result, the present study may have underestimated CHIP prevalence because of shallow sequencing depth.
“This inconsistency is a common challenge in CH population studies due to the lack of standardized methodologies and the frequent reliance on preexisting data not originally intended for CH detection,” Dr. Takahashi and Ms. Shah said.
Even so, despite the “heavily context-dependent” nature of these reported risks, the body of evidence to date now offers a convincing biological rationale linking CH with cancer development and outcomes, they added.