Abstract P2-06-03: The BRCA1 promoter methylation is one of the mechanisms of th BRCA1 dysfunction of triple-negative breast cancer

21083 Background: While BRCA1 germline mutations are uncommon, and contribute to fewer than 5% of breast cancer cases, epigenetic alterations in BRCA1 occur more frequently. BRCA1 promoter methylation has been detected in 10–30% of breast tumors. Given the role of BRCA1 in DNA repair and cell cycle regulation, we hypothesize that cells with decreased expression of BRCA1 secondary to promoter methylation will be sensitive to DNA damaging agents and resistant to microtubule inhibitors, as has previously been shown for cells deficient in BRCA1 secondary to mutation. Methods: BRCA1 methylation was determined using methylation specific PCR (MSP) as previously described (Wei et al, Cancer Research 2005). The relative sensitivities of BRCA1 methylated, mutated and competent cells to cisplatin and paclitaxel were determined in five representative breast cancer cell lines using the AlamarBlue cytotoxicity assay. Exponentially growing cells were treated with increasing concentrations of cisplatin and paclitaxel for 96 hours. IC50 values and 95% confidence intervals (CI) were calculated from sigmoidal dose response curves fitted with SAS 9.1 Proc NLIN. Western blot analysis for BRCA1 was performed on each cell line. Results: Conclusions: Only one of the two BRCA1 methylated cell lines studied (UACC3199) was sensitive to cisplatin and resistant to paclitaxel, as hypothesized. While both cell lines are methylated, western blot analysis revealed that both express BRCA1, but to a lesser degree than unmethylated cells. BRCA1 methylation, as assessed by non-quantitative MSP, does not correlate with sensitivity to cisplatin and resistance to paclitaxel. Quantification of BRCA1 promoter methylation may better predict chemosensitivity. Identification of the degree of BRCA1 methylation which does correlates with sensitivity to cisplatin and resistance to paclitaxel could improve treatment selection for patients with breast cancer. This work was supported by the US Army Grant W81XWH-04–1-0545. [Table: see text] No significant financial relationships to disclose.

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Molecular classification with NanoString nCounter system in triple-negative breast cancer.

Journal of Clinical Oncology ◽

10.1200/jco.2017.35.15_suppl.e23198 ◽

2017 ◽

Vol 35 (15_suppl) ◽

pp. e23198-e23198

Author(s):

Sung Gwe Ahn ◽

Seung Joon Kim ◽

Hak Woo Lee ◽

Hyo Jeong Yoon ◽

Chungyeul Kim ◽

...

Keyword(s):

Breast Cancer ◽

Triple Negative Breast Cancer ◽

Drug Response ◽

Triple Negative ◽

Molecular Classification ◽

Severance Hospital ◽

Brca1 Promoter Methylation ◽

Pearson's R ◽

Pearson’S R

e23198 Background: Previous studies have shown that several distinct subtypes identified by gene expression profiling (GEP) consisted of triple-negative breast cancer (TNBC). Compared with the subtypes defined by GEP, we developed molecular classification with NanoString nCounter system in TNBC. Methods: GEP was conducted on 188 FFPE containing chemotherapy-naïve TNBC tumors collected at Gangnam Severance Hospital. To select core genes for classification, other 120 samples from public GEP database were used. Correlation between nCounter system and GEP using identical RNA was done. In a part of tumors, BRCA1 methylation, homologous recombination deficiency (HRD) assay, and drug response assay with ATP was comprehensively assessed. Results: To classify TNBC into 4 major subtypes (Basal-like: BL, Luminal androgen receptor: LAR, Mesenchymal: M, and Immune-modulatory: IM) according to the Vanderbilt classification, we selected 110 genes in 220 samples with GEP (100 from Gangnam Severance Hospital and 120 from public database). In other 88 samples, the classification with the 110 genes were validated. In 149 tumors excluding UNS subtype by the Vanderbilt, a correlation between 110 genes-classification and the Vanderbilt system was 74.4% (111 of 149, Pearson’s R = 0.726). In 180 tumors with GEP and nCounter assay, a correlation between them was 85.0% (153 of 180, Pearson’s R = 0.827). Compared with tumors of the IM type by 110-genes, the recurrence-free survival was significantly reduced in tumors of the non-IM type by 110-genes ( P= 0.049). In cases with BRCA1 methylation test (n = 147), a significant higher rate of BRCA1 promoter methylation was found in BL type by nCounter system (BL: 41.0% vs. non-BL: 19.4%). In cases with HRD test, a significant lower rate of HRD was found in nCounter-identified LAR type (LAR: 0% vs. non-LAR: 79.3%). In patients with in vitro drug response assay with cisplatin (n = 36), tumors with nCounter-BL had a significant higher responsiveness than tumors with others ( P= 0.028). Conclusions: Our work shows the feasibility of molecular classification with nCounter system in TNBC. Future study warrants the clinical utility of this classification to guide the subtype-specific therapy in patients with TNBC.

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