Abstract P1-08-40: BRCA-1 promotor methylation and p53 mutation in triple-negative breast cancer patients refrectory to taxane-based neoadjuvant chemotherapy

Abstract

Abstract Introduction Triple-negative breast cancer (TNBC) without pathological complete response (pCR) to neoadjuvant chemotherapy (NAC) is associated with high risk of disease recurrence. In ABCSG trials 14 and 24, concomitant epirubicin plus docetaxel (+/- capecitabine) was used as NAC regimen; patients (pts) without pCR routinely received another 4-8 cycles of adjuvant CMF. Tumours harbouring BRCA-1 germline mutations are apparently less responsive to taxane-based chemotherapy, while sensitivity to DNA-damaging agents is retained. In sporadic TNBC, BRCA-1 promotor methylation is frequently observed; this may also result in an impaired activity of genetic repair mechanisms. Therefore, we investigated the effect of adjuvant CMF as salvage therapy in pts with or without BRCA-1 promotor methylation who did not achieve pCR to taxane-based (cyclophosphamide-free) NAC. Moreover, the predictive role of TP53 mutations was investigated in these tumours. Methods All pts with TNBC refractory to taxane-based NAC who received adjuvant CMF were included. DNA was extracted from formalin-fixed paraffin-embedded tissue samples with the Qiagen DNA FFPE Tissue Kit® and purified. For determining BRCA1 promoter methylation status, DNA was bisulfite-treated; the TaqMan® assay was used in order to perform a quantitative methylation-specific PCR. DNA quantity was normalized using Actin-b. For the investigation of TP53 mutations in exons 4-9, purified DNA was PCR amplified, sequenced by Sanger sequencing and results were analyzed with SeqScape® software version 2.7. Mutations were validated using the IARC p53 database. Results Twenty-four pts, median age 47 years, were available for this analysis. In 10/24 pts (41.7%), a BRCA-1 promotor methylation was detected; TP53 mutations were observed in 16/24 pts (66.7%). At a median follow-up of 27.5 months, 2/10 pts (20%) with BRCA-1 promotor metyhlation had a disease-free survival (DFS) event, as compared to 9/14 (64.3%) in the non-methylated group (p = 0.0472; Fisher's exact test). Kaplan Meier estimation of disease-free survival (DFS) in the non-methylated group was 16 months (95% CI 0.0-41.73) and was not reached in the methylated group (n.s.). TP53 mutation was neither associated with increased risk of disease recurrence nor with DFS. No correlation was observed between BRCA-1 promotor methylation and TP53 mutation; still, all methylated samples were exclusively affected be missense and nonsense mutations. Conclusions Adjuvant CMF is of limited activity in TNBC refractory to taxane-based NAC. Still, in breast cancer harbouring BRCA-1 promotor methylation, a significant decrease of DFS events was observed. TP53 mutation status on the other hand, was not associated with outcome; while no correlation was found between BRCA-1 promotor methylation and TP53 mutation status, we only observed missense and non-sense mutations in methylated samples. In conclusion, tumours harbouring BRCA-1 promotor methylation are apparently sensitive to DNA damage caused by cyclophosphamide. Further clinical validation of this concept is warranted. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-08-40.