title: Genomic aberrations in normal tissue adjacent to HER2-amplified breast cancers: field cancerization or contaminating tumor cells?
abstract: Field cancerization effects as well as isolated tumor cell foci extending well beyond the invasive tumor margin have been described previously to account for local recurrence rates following breast conserving surgery despite adequate surgical margins and breast radiotherapy. To look for evidence of possible tumor cell contamination or field cancerization by genetic effects, a pilot study (Study 1: 12 sample pairs) followed by a verification study (Study 2: 20 sample pairs) were performed on DNA extracted from HER2-positive breast tumors and matching normal adjacent mammary tissue samples excised 1-3 cm beyond the invasive tumor margin. High-resolution molecular inversion probe (MIP) arrays were used to compare genomic copy number variations, including increased HER2 gene copies, between the paired samples; as well, a detailed histologic and immunohistochemical (IHC) re-evaluation of all Study 2 samples was performed blinded to the genomic results to characterize the adjacent normal tissue composition bracketing the DNA-extracted samples. Overall, 14/32 (44 %) sample pairs from both studies produced genome-wide evidence of genetic aberrations including HER2 copy number gains within the adjacent normal tissue samples. The observed single-parental origin of monoallelic HER2 amplicon haplotypes shared by informative tumor-normal pairs, as well as commonly gained loci elsewhere on 17q, suggested the presence of contaminating tumor cells in the genomically aberrant normal samples. Histologic and IHC analyses identified occult 25-200 μm tumor cell clusters overexpressing HER2 scattered in more than half, but not all, of the genomically aberrant normal samples re-evaluated, but in none of the genomically normal samples. These genomic and microscopic findings support the conclusion that tumor cell contamination rather than genetic field cancerization represents the likeliest cause of local clinical recurrence rates following breast conserving surgery, and mandate caution in assuming the genomic normalcy of histologically benign appearing peritumor breast tissue.
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Anguraj
authors.initials: A
authors.lastname: Sadanandam
authors.forename: Aseem
authors.initials: A
authors.lastname: Lal
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Benz
authors.forename: Serenella
authors.initials: S
authors.lastname: Eppenberger-Castori
authors.forename: Gary
authors.initials: G
authors.lastname: Scott
authors.forename: Joe W
authors.initials: JW
authors.lastname: Gray
authors.forename: Paul
authors.initials: P
authors.lastname: Spellman
authors.forename: Fred
authors.initials: F
authors.lastname: Waldman
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Benz
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology*; D056915:DNA Copy Number Variations; D005260:Female; D006801:Humans; D008875:Middle Aged; D010865:Pilot Projects; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism; D012016:Reference Values; D059016:Tumor Microenvironment / Q000235:genetics
chemical_list: D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human