In an analysis of 31,717 cancer cases and 26,136 cancer-free controls
from 13 genome-wide association studies, we observed large chromosomal
abnormalities in a subset of clones in DNA obtained from blood or buccal
samples. We observed mosaic abnormalities, either aneuploidy or
copy-neutral loss of heterozygosity, of > 2 Mb in size in autosomes of
517 individuals (0.89%), with abnormal cell proportions of between 7%
and 95%. In cancer-free individuals, frequency increased with age, from
0.23% under 50 years to 1.91% between 75 and 79 years (P = 4.8 x
10(-8)). Mosaic abnormalities were more frequent in individuals with
solid tumors (0.97% versus 0.74% in cancer-free individuals; odds
ratio (OR) = 1.25; P = 0.016), with stronger association with cases who
had DNA collected before diagnosis or treatment (OR = 1.45; P = 0.0005).
Detectable mosaicism was also more common in individuals for whom DNA
was collected at least 1 year before diagnosis with leukemia compared to
cancer-free individuals (OR = 35.4; P = 3.8 x 10(-11)). These findings
underscore the time-dependent nature of somatic events in the etiology
of cancer and potentially other late-onset diseases
