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Abstract S4-04: Lobular carcinoma in situ displays intra-lesion genetic heterogeneity and its progression to invasive disease involves clonal selection and variations in mutational processes. Cancer Res 2016. [DOI: 10.1158/1538-7445.sabcs15-s4-04] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Introduction: Lobular carcinoma in situ (LCIS) is considered both a risk factor and non-obligate precursor of invasive breast cancer. We sought to determine the genomic landscape of LCIS and the mutational processes involved in the clonal evolution and progression from LCIS to ductal carcinoma in situ (DCIS) and invasive lobular carcinoma (ILC).
Methods: Patients with a history of LCIS undergoing therapeutic or prophylactic mastectomy were prospectively enrolled in an IRB approved protocol. Frozen tissue blocks were collected, screened for lesions of interest (LCIS, DCIS, ILC, invasive ductal carcinomas (IDC)) and subjected to microdissection and DNA/RNA extraction. Matched germline DNA was available for all cases. Whole exome sequencing was performed on a HiSeq2000 and data were aligned to the reference human genome and processed using GATK. Single nucleotide variants (SNVs) and small insertions/deletions were identified using MuTect and Varscan, respectively. Purity and ploidy estimates were calculated using ABSOLUTE. Clonal frequencies were estimated using Pyclone and the clonal structure of each sample was reconstructed using SubcloneSeeker. Shannon index and Simpson index metrics were used to calculate heterogeneity levels. Mutational signatures were defined according to their mutational trinucleotide context, and the expression levels of APOBEC gene family members were assessed by quantitative reverse transcription (qRT)-PCR.
Results: 30 LCIS, 10 ILCs, 7 DCIS and 5 IDCs from 15 patients qualified for data analysis. CDH1 was the most frequently mutated gene and found to be targeted by mutations in 26 LCIS samples (23 somatic, 3 germline). The repertoire of somatic mutations in LCIS was similar to that of luminal A breast cancers, with the exception of the significantly higher frequency of CDH1 mutations and the lower prevalence of TP53 mutations. ILCs were clonally related to at least one LCIS in 10 patients, and in 3/7 patients, DCIS was clonally related to at least one LCIS. Clonal composition analysis revealed that the presence of a minor clone(s) in LCIS, and the levels of intra-tumor genetic heterogeneity were significantly higher in LCIS clonally related with DCIS/ILC than in LCIS unrelated to DCIS/ILC. In two cases, a minor LCIS subclone constituted the major clone in the associated DCIS/ILC. A comparative analysis of the mutational signatures in the truncal and branch mutations of these cases revealed that whilst the truncal mutations displayed an aging signature, branch mutations were enriched for the APOBEC signature. qRT-PCR analysis demonstrated that cases displaying the APOBEC signature also harbored significantly higher levels of APOBEC3B expression than samples with the aging signature.
Conclusions: LCIS displays intra-lesion genetic heterogeneity, and the progression from LCIS to DCIS or ILC may involve the selection of clones resulting from distinct mutational processes during clonal evolution. Our findings also suggest that cytodine deamination driven by the overexpression of APOBEC3B may drive the progression of LCIS to DCIS/ILC in a subset of cases.
Citation Format: Reis-Filho JS, Schizas M, Piscuoglio S, Sakr RA, Ng CKY, Lim RS, Carniello JVS, Towers R, Martelotto L, Giri DD, de Andrade VP, Viale A, Solit DB, Weigelt B, King TA. Lobular carcinoma in situ displays intra-lesion genetic heterogeneity and its progression to invasive disease involves clonal selection and variations in mutational processes. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr S4-04.
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Abstract 2971: Whole exome sequencing reveals heterogeneity within lobular carcinoma in situ (LCIS) and clonal selection in the progression to malignant lesions. Cancer Res 2015. [DOI: 10.1158/1538-7445.am2015-2971] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
INTRODUCTION: Lobular carcinoma in situ (LCIS) is considered both a risk factor and non-obligate precursor of low-grade estrogen receptor-positive breast cancer. We sought to define the mutational repertoire, subclone complexity and heterogeneity of LCIS, and whether invasive lobular carcinomas (ILCs) would stem from specific subclones within a LCIS.
METHODS: Patients with a history of LCIS undergoing therapeutic or prophylactic mastectomy were prospectively enrolled in an IRB approved protocol. Frozen tissue blocks were collected, screened for lesions of interest (LCIS, ductal carcinoma in situ (DCIS), ILC, invasive ductal carcinoma (IDC)) and subject to microdissection and DNA extraction. Matched germline DNA was available for all cases. Whole exome sequencing was performed on a HiSeq2000 (Illumina) and data were aligned to the reference human genome hg19 and processed using GATK. SNVs were called using MuTect, and indels were called using a combination of Varscan and Strelka. Purity and ploidy estimates were calculated by ABSOLUTE. Clonal frequencies were estimated using Pyclone.
RESULTS: 30 LCIS, 10 ILCs, 6 IDCs and 7 DCIS from 15 patients qualified for data analysis, resulting in 18 LCIS-ILC pairs, 22 LCIS-LCIS pairs, 12 LCIS-DCIS pairs, and 14 LCIS-IDC pairs for comparison. 9/18 (50%) LCIS-ILC pairs and 8/22 (36%) LCIS-LCIS pairs were clonally related, supported by several shared mutations (median 18, range 7-81 for LCIS-ILC; median 14, range 5-22 for LCIS-LCIS). All related LCIS-ILC pairs and 6/8 related LCIS-LCIS pairs shared a pathogenic CDH1 mutation; 75% of related LCIS-ILC pairs also shared a PIK3CA hotspot mutation. 7/12 (58%) LCIS-DCIS pairs were found to be clonally related but the number of shared mutations was generally lower than that found in LCIS-ILC pairs (median 9, range 2-11). No evidence of a clonal relationship was found in any of the LCIS-IDC pairs tested. Clonal composition analysis revealed that samples of LCIS display intra-lesion genetic heterogeneity in the form of the presence of a minor clone in 70% of cases. In one case, the LCIS minor subclone (∼15%) constituted the major clone in the ILC and in another case the LCIS minor subclone constituted the major clone in the associated DCIS. The majority of the clonally related lesions were located in the same quadrant of the breast, however evidence of clonality was found in 5 LCIS-LCIS and 3 LCIS-DCIS pairs located in separate quadrants of the breast.
CONCLUSIONS: Intra-lesion genetic heterogeneity is a common phenomenon in LCIS. The dominant clone of a LCIS may not always be the clone directly involved in the progression to malignancy. The spatial relationships of clonally related lesions in this study suggest that anatomy does not always infer clonality, as lesions located in separate quadrants of the breast may be clonally related.
Citation Format: Michail Schizas, Rita A. Sakr, Britta Weigelt, Charlotte KY Ng, Jose Victor S. Carniello, Dilip Giri, Salvatore Piscuoglio, Luciano G. Martelotto, Russell Towers, Victor P. Andrade, Raymond Lim, David B. Solit, Jorge S. Reis-Filho, Tari A. King. Whole exome sequencing reveals heterogeneity within lobular carcinoma in situ (LCIS) and clonal selection in the progression to malignant lesions. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2971. doi:10.1158/1538-7445.AM2015-2971
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