Fig. 3: Developmental mosaicism is demonstrated by mutated normal lung cells and early common ancestors.
From: Developmental mosaicism underlying EGFR-mutant lung cancer presenting with multiple primary tumors
a, Detection of the L858R EGFR mutation using ddPCR in cases where the tumor harbors the L858R mutation (patients (Pt) 8–10) compared with cases where the tumor contains another EGFR mutation (negative control (Neg. ctrl), patients 1 and 7). The VAF for tumors is on the left y axis whereas the lower VAF in normal samples is on the right y axis (n = 2 tumor and 11 normal samples (independent microdissection regions) for patient 8; 4 tumor and 8 normal samples for patient 9; 12 tumor and 9 normal samples for patient 10; 3 tumor and 6 normal samples for patient 1; and 2 tumor and 9 normal samples for patient 7). b, A schematic showing the relationship between divergence from zygote and divergence between tumors. c, Schematic of poly(G) genotype analysis method, based on ref. 38. Samples collected from a single patient have poly(G) sites that may have undergone slippage due to hypermutability. The assay detects these indels and measures their mean length change compared with normal tissue. The correlation between the two tumors across all poly(G) sites is represented by Pearson’s correlation coefficient (r). d, Heatmap showing the mean distance from normal lung for each poly(G) hypermutable region, for each tumor from patient III-1. Tumors that have similar patterns are more closely related than tumors that have different patterns. e, Phylogenetic tree of patient III-1 based on the poly(G) analysis. The tree is rooted at the germline sample: i shows only samples from the first resection and ii samples from the second resection plus recurring sample T5. f, Correlation plots between tumors from patient III-1. The dots represent the mean length from normal at each poly(G) location (n = 26 poly(G) loci). The r estimates what fraction of cell divisions were shared between the tumor pair before divergence. The gray shading represents the 95% CI. g, Poly(G) relatedness between tumor pairs. Each point represents the poly(G) evolutionary distance between two tumors from cases that are unrelated (different individuals), mosaic or metastatic (classification based on WES analysis of exonic mutations). The dotted line represents that correlation coefficient >95% of the unrelated tumor pairs. Boxplot elements: center line, median; box limits, lower and upper quartiles; whiskers, lowest and highest value within 1.5× the IQR. P values are a Holm–Bonferroni-corrected, post-hoc Dunn’s test after a significant Kruskal–Wallis test. The arrow is the tumor pair from metastatic patient 3. NS, Not significant. (n = 443 interpatient tumor pair comparisons across eight patients for the unrelated analysis; n = 7 intrapatient tumor pair comparisons within four mosaic patients for the mosaic analysis; and n = 29 intrapatient tumor pair comparisons within two metastatic patients for the metastatic analysis).
