Concordant DNA methylation in synchronous colorectal carcinomas

Abstract

Epigenetic changes have been proposed as mediators of the field defect in colorectal carcinogenesis, which has implications for risk assessment and cancer prevention. As a test of this hypothesis, we evaluated the methylation status of eight genes (MINT1, 2, 31, MLH1, p16, p14, MGMT, and ESR1), as well as BRAF and KRAS mutations, in 57 multiple colorectal neoplasias (M-CRN) and compared these to 69 solitary colorectal cancers (S-CRC). There were no significant differences in methylation between M-CRNs and S-CRCs except for p14 and MGMT that was significantly higher in M-CRNs than S-CRCs (16.1% versus 9.3%; 26.5% versus 17.3%, respectively; P < 0.05). We found significant (P < 0.05) correlations for MINT1 (r = 0.8), p16 (r = 0.8), MLH1 (r = 0.9), and MGMT (r = 0.6) methylation between tumors pairs of the same site (proximal/proximal and distal/distal). KRAS showed no concordance in mutations. BRAF mutation showed concordance in proximal site pairs but was discordant in different site pairs. Histologically, eight of 10 paired cancers with similar locations were concordant for a cribriform glandular configuration. We conclude that synchronous colorectal tumors of the same site are highly concordant for methylation of multiple genes, BRAF mutations, and a cribriform glandular configuration, all consistent with a patient-specific predisposition to particular subtypes of colorectal cancers. Screening for and secondary prevention of colon cancer should take this fact into account.

Fig. 1

Distribution of methylation levels of eight genes/CpG islands in cancer (A) and colonic mucosa adjacent to cancer (B). Each dot represents the methylation level of an individual sample. Horizontal lines, mean methylation levels for each group. #, P = 0.0004; ¶, P = 0.037. M, M-CRN; S, S-CRCs. *, regular assay; **, sensitive assay.

Fig. 2

Methylation status of seven CpG islands, mutation status of KRAS and BRAF, and histologic findings in synchronous colon tumors. Each column represents a separate gene locus indicated on top. Each row represents a synchronous colorectal neoplasm. White, average methylation densities less than <15%; gray, 15–50% methylation; black, methylation greater than 50%. Black squares, presence of mutations; white squares, absence of mutations. The top group is patients with two proximal CRCs, the middle group is patients with two distal CRCs, and the bottom group is patients with proximal and distal CRCs. C, cancer; A, adenoma; P, proximal colon; D, distal colon; CGC, cribriform glandular configuration; WD, well-differentiated adenocarcinoma; MD, moderately differentiated adenocarcinoma; PD, poorly differentiated adenocarcinoma; TV, tubulovillous adenoma; T, tubular adenoma; AD, adenoma; NA, not applicable.

Fig. 2

Methylation status of seven CpG islands, mutation status of KRAS and BRAF, and histologic findings in synchronous colon tumors. Each column represents a separate gene locus indicated on top. Each row represents a synchronous colorectal neoplasm. White, average methylation densities less than <15%; gray, 15–50% methylation; black, methylation greater than 50%. Black squares, presence of mutations; white squares, absence of mutations. The top group is patients with two proximal CRCs, the middle group is patients with two distal CRCs, and the bottom group is patients with proximal and distal CRCs. C, cancer; A, adenoma; P, proximal colon; D, distal colon; CGC, cribriform glandular configuration; WD, well-differentiated adenocarcinoma; MD, moderately differentiated adenocarcinoma; PD, poorly differentiated adenocarcinoma; TV, tubulovillous adenoma; T, tubular adenoma; AD, adenoma; NA, not applicable.

Fig. 3

Correlations in methylation levels of MINT1 (A, E, I, and M), p16 (B, F, J, and N), MLH1 (C, G, K, and O), and MGMT (D, H, L, and P) in synchronous tumors and sporadic cancers. We observed significant correlations in methylation of these four genes in synchronous tumors with the same location (A–D) but not in paired tumors selected from S-CRCs (I–L). Moreover, there were significant correlations in p16, MLH1, and MGMT methylation between proximal synchronous tumors in the same patients (F–H). However, we observed no significant correlations between proximal S-CRCs (M–P). PP+DD, case with two proximal tumors or two distal tumors; PP, case with two proximal tumors.

Fig. 4

Histopathology in synchronous CRCs with/without CIMP. A, B, and C, cribriform glandular architecture as follows: a gland with a comedo-like pattern and bridging of cells across the lumen has spaces filled with necrotic debris. These tumors (A, B, and C) showed CIMP, whereas a tumor without cribriform glandular architecture did not (D). A and B, histologic findings of a patient with two proximal CRCs; C and D, histologic findings in a patient with a proximal and a distal CRC, respectively.