title: Identifying allelic loss and homozygous deletions in pancreatic cancer without matched normals using high-density single-nucleotide polymorphism arrays.
abstract: Recent advances in oligonucleotide arrays and whole-genome complexity reduction data analysis now permit the evaluation of tens of thousands of single-nucleotide polymorphisms simultaneously for a genome-wide analysis of allelic status. Using these arrays, we created high-resolution allelotype maps of 26 pancreatic cancer cell lines. The areas of heterozygosity implicitly served to reveal regions of allelic loss. The array-derived maps were verified by a panel of 317 microsatellite markers used in a subset of seven samples, showing a 97.1% concordance between heterozygous calls. Three matched tumor/normal pairs were used to estimate the false-negative and potential false-positive rates for identifying loss of heterozygosity: 3.6 regions (average minimal region of loss, 720,228 bp) and 2.3 regions (average heterozygous gap distance, 4,434,994 bp) per genome, respectively. Genomic fractional allelic loss calculations showed that cumulative levels of allelic loss ranged widely from 17.1% to 79.9% of the haploid genome length. Regional increases in "NoCall" frequencies combined with copy number loss estimates were used to identify 41 homozygous deletions (19 first reports), implicating an additional 13 regions disrupted in pancreatic cancer. Unexpectedly, 23 of these occurred in just two lines (BxPc3 and MiaPaCa2), suggesting the existence of at least two subclasses of chromosomal instability (CIN) patterns, distinguished here by allelic loss and copy number changes (original CIN) and those also highly enriched in the genomic "holes" of homozygous deletions (holey CIN). This study provides previously unavailable high-resolution allelotype and deletion breakpoint maps in widely shared pancreatic cancer cell lines and effectively eliminates the need for matched normal tissue to define informative loci.
authors.affiliation: Department of Oncology,The Sol Goldman Pancreatic Cancer Research Center at the Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins Medical Institutes, Baltimore, MD 21231, USA. ecalhou2@jhmi.edu
authors.forename: Eric S
authors.initials: ES
authors.lastname: Calhoun
authors.forename: Tomas
authors.initials: T
authors.lastname: Hucl
authors.forename: Eike
authors.initials: E
authors.lastname: Gallmeier
authors.forename: Kristen M
authors.initials: KM
authors.lastname: West
authors.forename: Dan E
authors.initials: DE
authors.lastname: Arking
authors.forename: Anirban
authors.initials: A
authors.lastname: Maitra
authors.forename: Christine A
authors.initials: CA
authors.lastname: Iacobuzio-Donahue
authors.forename: Aravinda
authors.initials: A
authors.lastname: Chakravarti
authors.forename: Ralph H
authors.initials: RH
authors.lastname: Hruban
authors.forename: Scott E
authors.initials: SE
authors.lastname: Kern
mesh_terms: D045744:Cell Line, Tumor; D006801:Humans; D019656:Loss of Heterozygosity; D018895:Microsatellite Repeats; D020411:Oligonucleotide Array Sequence Analysis; D010190:Pancreatic Neoplasms / Q000235:genetics*; D020641:Polymorphism, Single Nucleotide; D012016:Reference Values; D015203:Reproducibility of Results; D017384:Sequence Deletion