Clonality assessment and clonal ordering of individual neoplastic crypts shows polyclonality of colorectal adenomas.
OBJECTIVE
According to the somatic mutation theory, monoclonal colorectal lesions arise from sequential mutations in the progeny of a single stem cell. However, studies in a sex chromosome mixoploid mosaic (XO/XY) patient indicated that colorectal adenomas were polyclonal. We assessed adenoma clonality on an individual crypt basis and completed a genetic dependency analysis in carcinomas-in-adenomas to assess mutation order and timing.


METHODS
Polyp samples were analyzed from the XO/XY individual, patients with familial adenomatous polyposis and attenuated familial adenomatous polyposis, patients with small sporadic adenomas, and patients with sporadic carcinoma-in-adenomas. Clonality was analyzed using X/Y chromosome fluorescence in situ hybridization, analysis of 5q loss of heterozygosity in XO/XY tissue, and sequencing of adenomatous polyposis coli. Individual crypts and different phenotypic areas of carcinoma-in-adenoma lesions were analyzed for mutations in adenomatous polyposis coli, p53, and K-RAS; loss of heterozygosity at 5q, 17p, and 18q; and aneuploidy. Phylogenetic trees were constructed.


RESULTS
All familial adenomatous polyposis-associated adenomas and some sporadic lesions had polyclonal genetic defects. Some independent clones appeared to be maintained in advanced adenomas. No clear obligate order of genetic events was established. Top-down growth of dysplastic tissue into neighboring crypts was a possible mechanism of clonal competition.


CONCLUSIONS
Human colorectal microadenomas are polyclonal and may arise from a combination of host genetic features, mucosal exposures, and active crypt interactions. Analyses of tumor phylogenies show that most lesions undergo intermittent genetic homogenization, but heterotypic mutation patterns indicate that independent clonal evolution can occur throughout adenoma development. Based on observations of clonal ordering the requirement and timing of genetic events during neoplastic progression may be more variable than previously thought.
Thirlwell
Christina
C
London Research Institute, Cancer Research, London, United Kingdom.
Will
Olivia C C
OC
Domingo
E
E
Graham
Trevor A
TA
McDonald
Stuart A C
SA
Oukrif
Dahmane
D
Jeffrey
Rosemary
R
Gorman
Maggie
M
Rodriguez-Justo
Manuel
M
Chin-Aleong
Joanne
J
Clark
Sue K
SK
Novelli
Marco R
MR
Jankowski
Janusz A
JA
Wright
Nicholas A
NA
Tomlinson
Ian P M
IP
Leedham
Simon J
SJ
D000236:Adenoma / Q000209:etiology / Q000235:genetics* / Q000473:pathology; D015179:Colorectal Neoplasms / Q000209:etiology / Q000235:genetics* / Q000473:pathology; D017491:Genes, APC; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D019656:Loss of Heterozygosity; D009154:Mutation