Abstract P2-10-05: The impact of <i>TP53</i> mutation and pathological response to neoadjuvant chemotherapy on triple negative breast cancer outcomes
Authors: Z Mitri, C-H Lin, KR Hess, A Thompson, O Lichtarge, R Hubbard, C Fu, WF Symmans, SL Moulder-Thompson
Journal: Cancer Research (2018)

Abstract Background: Triple Negative Breast Cancer (TNBC) accounts for 15-20% of breast cancers, and has a poor prognosis compared with hormone receptor-positive or HER2-amplified disease. There is currently no targeted therapy to salvage chemotherapy resistant TNBC confirming a need for predictive biomarkers of sensitivity to therapy. This study aimed to evaluate the impact of TP53 mutations, common in TNBC, on sensitivity to therapy and patient outcomes. Methods: TNBC samples (pretreatment biopsies and surgical specimens, n=106) had annotated response to standardized anthracycline/taxane based neoadjuvant chemotherapy (NACT) and 3-year survival data, by which time most recurrences occur in TNBC. RNAseq was performed using Illumina HiSeq with mRNA library preparation protocol to identify TP53 mutations, which were then scored using the Evolutionary Action Score (EAS), a novel computational model shown to be successful at identifying deleterious mutations. This work was supported by an ASCO Conquer Cancer Foundation Young Investigator Award grant. Results: 106 TNBC patients were enrolled on this study, 14 had stage I, 65 stage II, and 24 had stage III disease. 64 patient samples have been analyzed to date, of which 39 (61%) harbored a TP53 mutation, and 24 (38%) were TP53 wildtype. Pathologic complete response (pCR) and survival Of 47 patients who received NACT, 14 (30%) achieved a pCR, and 33 (70%) had residual disease (RD). Patients who achieved a pCR had a significantly better 3-year recurrence free survival (RFS) (100% vs 59%, p=0.011) and overall survival (OS) (100% vs 62%, p-0.01) compared to patients who had residual disease. TP53 status and pCR The rate of pCR was significantly higher in the TP53 mutant group (11/29, 38%) compared to TP53 wildtype (2/17, 12%) TNBC (OR = 4.6, (0.9, 24), p = 0.046). Patients with wild-type and mutant TP53 TNBC who achieved a pCR had excellent 3-year RFS and OS at 100%. Among patients with RD, TP53 wild-type TNBC exhibited a non-significant trend towards higher 3-year RFS (72% vs 49%,HR = 2.5 (0.8, 8.0) p = 0.12) and OS (79% vs 48%,HR = 2.6 (0.8, 8.4) p = 0.11) compared to TP53 mutant TNBC. TP53 status and survival The 3-year OS for TP53 mutant TNBC was 72%, compared to 86% for TP53 wildtype TNBC (HR = 1.5 (0.5, 4.3), p = 0.48). There was no difference in 3-year RFS between the two groups. TP53 EAS and survival Among 39 non-silent TP53 mutant cases, EAS ranged from 42.3 to 100 with a median score of 87.6. The 3-year OS for patients with EAS ≥86.7 was 73%, compared to 74% for patients with EAS &amp;lt;86.7 (HR 0.8 (0.2, 3.0), p=0.78). When separated into tertiles, the 3-year OS rates were 75%, 68%, and 77% for the lower, middle, and upper thirds respectively. The 3-year OS rates for TNBC with EAS = 0 (TP53 wildtype or silent TP53 mutation) was 87%. Conclusion: TP53 mutations were associated with a higher chance of achieving a pCR; NACT Patients who achieved a pCR to NACT had excellent outcomes, regardless of TP53 mutation status. In patients with RD following NACT, TP53 mutant TNBC had a trend towards worse outcomes compared to TP53 wild-type TNBC. Larger cohorts are required to further evaluate the impact of TP53 mutations and TP53 EAS on survival outcomes in TNBC. Citation Format: Mitri Z, Lin C-H, Hess KR, Thompson A, Lichtarge O, Hubbard R, Fu C, Symmans WF, Moulder-Thompson SL. The impact of TP53 mutation and pathological response to neoadjuvant chemotherapy on triple negative breast cancer outcomes [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-10-05.