Neoplasms are thought to progress to cancer through genetic instability generating cellular diversity and clonal expansions driven by selection for mutations in cancer genes. Despite advances in the study of molecular biology of cancer genes, relatively little is known about evolutionary mechanisms that drive neoplastic progression. It is unknown, for example, which may be more predictive of future progression of a neoplasm: genetic homogenization of the neoplasm, possibly caused by a clonal expansion, or the accumulation of clonal diversity. Here, in a prospective study, we show that clonal diversity measures adapted from ecology and evolution can predict progression to adenocarcinoma in the premalignant condition known as Barrett's esophagus, even when controlling for established genetic risk factors, including lesions in TP53 (p53; ref. 6) and ploidy abnormalities. Progression to cancer through accumulation of clonal diversity, on which natural selection acts, may be a fundamental principle of neoplasia with important clinical implications.

Ulcerative colitis, a chronic inflammatory disease of the colon, is associated with a high risk of colorectal carcinoma that is thought to develop through genomic instability. We considered that the rapid cell turnover and oxidative injury observed in ulcerative colitis might accelerate telomere shortening, thereby increasing the potential of chromosomal ends to fuse, resulting in cycles of chromatin bridge breakage and fusion and chromosomal instability associated with tumor cell progression. Here we have used quantitative fluorescence in situ hybridization to compare chromosomal aberrations and telomere shortening in non-dysplastic mucosa taken from individuals affected by ulcerative colitis, either with (UC progressors) or without (UC non-progressors) dysplasia or cancer. Losses, but not gains, of chromosomal arms and centromeres are highly correlated with telomere shortening. Chromosomal losses are greater and telomeres are shorter in biopsy samples from UC progressors than in those from UC non-progressors or control individuals without ulcerative colitis. A mechanistic link between telomere shortening and chromosomal instability is supported by a higher frequency of anaphase bridges--an intermediate in the breakage and fusion of chromatin bridges--in UC progressors than in UC non-progressors or control individuals. Our study shows that telomere length is correlated with chromosomal instability in a precursor of human cancer.

Background:Telomeres are tandem repeated DNA sequences at the ends of every chromosome, which cap, stabilize, and prevent chromosome fusions and instability. Telomere regulation is an important mechanism in cellular proliferation and senescence in normal diploid and neoplastic cells. Quantitative methods to assess telomere lengths are essential to understanding how telomere dynamics play a role in these processes. Methods: Telomere lengths have been conventionally measured using terminal restriction fragment (TRF), quantitative fluorescence in situ hybridization (QFISH), and flow FISH. In this study, we have applied QFISH to measure average telomere lengths in cultured cells and human tissues of the GI tract. Importantly, this method can be used to analyze telomere lengths in sections using confocal microscopy. We describe and compare three image analysis algorithms: a simple pixel histogram calculation of background corrected fluorescence, a telomere spotfinding method, and a background curve subtraction algorithm. Results: Using normal human diploid fibroblasts (NHDF) either dropped on slides or sectioned after agar embedding, similar telomere length shortening is evident with increasing population doubling levels (PDLs), using peptide nucleic acid (PNA) and an N3Ј-P5Ј-phosphoamidate (PA) oligonucleotide probe for all three methods. Valida-