Mre11 Dysfunction Is Associated With Triple-Negative Breast Cancer and Confers Sensitivity to DNA Damaging Therapy

Volume 96  Number 2S  Supplement 2016 pathology groups on univariate and multivariate analyses (both P < 0.05). Hierarchical clustering within the training cohort produced 8 pathologybased radiomics signatures associated with OS. Of the 4 signatures that retained significance within the validation cohort, we focused on a signature comprised of highly reproducible features. Four radiomics features comprised this model: CT intensity global mean, standard deviation, and uniformity and gray level co-occurrence matrix homogeneity. On multivariate analysis adjusting for stage and adjuvant therapy, this model was significantly associated with OS in both cohorts (both P < 0.05). Conclusion: We present a NSCLC radiomics signature based on the local immune environment that may predictive implications especially with immunotherapy. We are currently working on application of this model to select patients for combined radiotherapy with checkpoint inhibitors. Author Disclosure: C. Tang: None. A. Amer: None. B. Hobbs: None. X. Li: None. C. Behrens: None. E. Para Cuentas: None. J. Rodriguez Canales: None. J.Y. Chang: None. D. Hong: Research Grant; Novartis, Genentech, Eisai, AstraZeneca, Pfizer, miRNA. J.W. Welsh: Research Grant; BMS, Merck, Varian, GSK, Mirnatherapeutics, Inc., Merck. Stock; Helios, Molecular Match. Stock Options; Oncoresponse, Reflexion Medical, Checkmate Pharmaceuticals. I. Wistuba: None. E.J. Koay: Research Grant; Phillips. Honoraria; Phillips.

95 Mre11 Dysfunction Is Associated With Triple-Negative Breast Cancer and Confers Sensitivity to DNA Damaging Therapy G.P. Gupta,1 A.Y. Ho,2 W. Feng,1 C. Fan,1 M. Akram,2 E. Brogi,2 S.N. Powell,2 C.M. Perou,1 Y.H. Wen,2 and J.H.J. Petrini2; 1University of North Carolina, Chapel Hill, NC, 2Memorial Sloan Kettering Cancer Center, New York, NY Purpose/Objective(s): Understanding the molecular basis for DNA damage response perturbations in human cancers is vital to improving the molecular precision of radiotherapy and chemotherapy. We have previously demonstrated that the DNA damage sensor Mre11 is a suppressor of breast tumorigenesis and is underexpressed in a subset of triple negative breast cancers (TNBC) that exhibits excellent clinical outcomes. The goals of this study were to develop a transcriptional signature associated with Mre11 dysfunction and evaluate its correlation with response to neoadjuvant chemotherapy (NAC) in clinical cohorts of breast cancer. Materials/Methods: RNA-seq of murine wild-type and Mre11 mutant breast cancers was performed, and differentially expressed genes were identified using Significance Analysis of Microarrays (SAM). For patient studies, immunohistochemistry (IHC) against human Mre11 was performed on tissue microarrays that contained triplicate cores of non-metastatic TNBC (ER/PR <1%; HER2 0/1+, or HER2 2+/FISH not amplified) from 271 patients. Tumors were classified as Mre11 low if <10% of cancer cells had detectable nuclear protein expression. A subset of Mre11 high and Mre11 low TNBC were confirmed by staining whole tissue sections and subject to RNA-seq analysis. SAM was performed to derive a gene signature associated with Mre11 low status, and intersected with the gene list obtained from the mouse model. This cross-species gene signature was incorporated into a cumulative Z-score based classifier and applied to a published cohort of gene expression data (GSE25066) representing 462 breast cancers with known response to NAC. Fisher’s exact test was used to calculate two-sided P values in 2 x 2 contingency table analyses. Results: Breast cancers that expressed the Mre11 low signature in the GSE25066 dataset were highly enriched for TNBC (16/25 vs. 170/462, P < 0.01), consistent with prior findings using Mre11 IHC. Sixteen out of 186 TNBCs (8.6%) in GSE25066 expressed the Mre11 low gene signature, which is highly concordant with the proportion of Mre11 low expressers identified in the IHC cohort (9.0%). Breast cancers that expressed the Mre11 low signature were significantly more likely to achieve pathological complete response (pCR) to NAC (10/24 vs. 81/238, P Z 0.014). Treatment of Mre11 mutant murine breast cancers also demonstrated hypersensitivity to specific DNA damaging agents relative to Mre11 wild type tumors.

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Conclusion: A gene signature associated with Mre11 dysfunction identifies a subset of breast cancers with increased rates of pCR to NAC. Together with results obtained from our Mre11 mutant breast cancer mouse model, these findings provide a mechanistic explanation for improved clinical outcomes in Mre11 low TNBC, and represent an opportunity for personalization of DNA damage-based therapy. Author Disclosure: G.P. Gupta: None. A.Y. Ho: None. W. Feng: None. C. Fan: None. M. Akram: None. E. Brogi: None. S.N. Powell: None. C.M. Perou: None. Y.H. Wen: None. J.H. Petrini: None.

96 Homologous Recombination Function Predicts Treatment Response in Head and Neck Squamous Cell Carcinoma S.A. Bhide,1 K. Thway,2 J. Lee,3 K.H. Wong,4 D.M. Gujral,5 S.H. Zaidi,6 K. Newbold,7 C.M. Nutting,4 and K. Harrington8; 1The Royal Marsden NHS Foundation Trust, Sutton and London, United Kingdom, 2Royal Marsden Hospital, London, United Kingdom, 3Institute of Cancer Research, London, United Kingdom, 4The Royal Marsden NHS Foundation Trust, Sutton, United Kingdom, 5Imperial College Healthcare NHS Trust, London, United Kingdom, 6The Royal Marsden Hospital, London, United Kingdom, 7Royal Marsden Hospital, Sutton, United Kingdom, 8The Institute of Cancer Research, Sutton, United Kingdom Purpose/Objective(s): Homologous recombination (HR) is a part of a complex DNA damage response pathway (DDR), functional assessment of which in tumors could help predict treatment sensitivity. The aim of this study was to investigate if defective repair of DNA double strand break (DSB) by HR pathway in HNSCC could be used as an early predictor of response following radical treatment. Materials/Methods: Punch biopsy of the tumor in patients with Stage III and IV SCC of the oropharynx was obtained 24 hours following induction chemotherapy (IC). Formalin-fixed paraffin embedded tumor blocks (FFPE) prepared from this sample and pre-treatment biopsies were stained for RAD51 and geminin (S-phase marker) for immunofluorescence and images obtained on confocal microscope. The percentage of gemininpositive cells that were also positive for RAD51 was calculated as the RAD51 score for both specimens. Difference between the RAD51 score for the two specimens was then computed to reflect the HR status. Patients with a percentage difference of 10% between the two samples were deemed to have repaired IC-induced DSBs, and were classified as HR proficient. Foci analyses were blinded to the time-point of the sample and all clinical data. Response at 3 months post-treatment and human papilloma virus (HPV) status (p16 IHC and RT-PCR, E6 mRNA) were assessed. Results: Samples from 13/15 patients recruited were available for analyses. The difference in in RAD51 score between pre and posteIC was statistically significant (median 12% and 50%, P < 0.001). Three samples were classified as HR proficient and 10 as HR deficient at 24 hours postIC. All of the 3 patients classified as HR proficient had partial response or progressive disease and the ten patients deemed HR deficient had a CR

Abstract 96; Table 1: Describes the HPV status, HR functional status, and treatment response. HPV status ve +ve ve ve +ve +ve +ve +ve +ve +ve ve ve +ve

Difference in RAD51 foci pre and post-IC (%)

HR status

Treatment response

31 25 7 3 62 44 71 74 27 72 3 27 57

Deficient Deficient Proficient Proficient Deficient Deficient Deficient Deficient Deficient Deficient Proficient Deficient Deficient

CR CR PR PR CR CR CR CR CR CR PR CR CR