Abstract P3-06-12: Genetic heterogeneity of DCIS is a predictor of invasive cancer

Background: Heterogeneity is a hallmark of human cancers that is apparent both between and within individual tumors. Intra-tumor heterogeneity provides the genetic fuel for natural selection in clonal evolution and cancer progression. Tumors with high levels of genetic heterogeneity are hypothesized to be more likely to progress to invasion and metastasis Methods: We measured the mutational loads from separate areas of pure DCIS and compared this to genetic heterogeneity in DCIS lesions that co-exist with invasive cancer, as a surrogate for progression. Cases of pure DCIS and DCIS diagnosed concurrent with invasive cancer were identified. Two areas of DCIS from each case a minimum of 0.8 cm apart and control tissues were macro-dissected and the DNA extracted from FFPE samples. To analyze the data, we developed new bioinformatics methods that allowed analysis of small amounts of degraded DNA extracted from FFPE samples across multiple regions. Our bioinformatics pipeline was optimized on a series of 28 independent technical replicates of the same DNA sample sequenced twice, as training tools to find the best filtering parameters. Results: Whole exome sequencing was performed on two geospatially separated blocks for each case (41 pure DCIS and 30 DCIS adjacent to invasive disease). Minimum coverage for inclusion in this study was 40X over at least 50% of the exome. We used the ratio of private mutations (only in 1 area) to public (found in both areas) mutations as a measure of intra-tumor heterogeneity. Overall mutational load of DCIS was not a significant predictor to progression; however notably, DCIS adjacent to invasive disease patients had a higher ratio of private/public mutations (heterogeneity) in coding domains (Mann-Whitney p=0.016. Functional analysis of mutated coding genes (DAVID 6.8) shows a statistically significant enrichment in signal transduction, olfactory receptors (G-protein-coupled receptors) and cell-matrix interactions in both tumor types, after FDR correction. DCIS adjacent to invasive disease had an enrichment of mutated genes involved in additional cellular functions such as microtubule activity (fold enrichment =7.6, FDR=0.002), protein-protein interactions (fold enrichment =3.65, FDR=5.11E-04) and extracellular matrix remodeling (fold enrichment =8.3, FDR=0.02). Conclusion: We present an approach to measure clonal heterogeneity using a bulk sequencing strategy applied to geospatially distinct foci of DCIS. Our findings suggest that functional heterogeneity may play an important evolutionary role as a driver for invasive progression. Citation Format: Fortunato A, Mallo D, King L, Hardman T, Hall A, Marks JR, Hwang S, Maley CC. Genetic heterogeneity of DCIS is a predictor of invasive cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-06-12.