Purpose: Blockade of the PD-1/PD-L1 axis emerged as a promising new therapeutic option for cancer that has resulted in lasting responses in metastatic renal, lung carcinomas, and melanomas. Tumor PD-L1 protein expression may predict response to drugs targeting this pathway. Measurement of PD-L1 protein is limited by the lack of standardized immunohistochemical methods and variable performance of antibodies. Our goal was to correlate PD-L1 mRNA expression with clinical variables in primary breast carcinomas.Experimental Design: The fluorescent RNAscope paired-primer assay was used to quantify in situ PD-L1 mRNA levels in 636 stage I-III breast carcinomas on two sets of tissue microarrays [YTMA128 (n ¼ 238) and YTMA201 (n ¼ 398)]. Tumor-infiltrating lymphocytes (TIL) were assessed by hematoxylin/eosin stain and quantitative fluorescence.Results: On YTMA128 and YTMA201, 55.7% and 59.5% of cases showed PD-L1 mRNA expression, respectively. Higher PD-L1 mRNA expression was significantly associated with increased TILs (P ¼ 0.04) but not with other clinical variables. Elevated TILs (scores 2 and 3þ) occurred in 16.5% on YTMA128 and 14.8% on YTMA201 and was associated with estrogen receptor-negative status (P ¼ 0.01 on YTMA128 and 0.0001 on YTMA201). PD-L1 mRNA expression was associated with longer recurrence-free survival (log-rank P ¼ 0.01), which remained significant in multivariate analysis including age, tumor size, histologic grade, nodal metastasis, hormone receptor, HER2 status, and the extent of TILs (HR, 0.268; CI, 0.099-0.721; P ¼ 0.009).Conclusions: PD-L1 mRNA expression is identified in nearly 60% of breast tumors and it is associated with increased TILs and improved recurrence-free survival. These observations support the evaluation of PD-

Summary Endocrine therapies for breast cancer that target the estrogen receptor (ER) are ineffective in the 25-30% of cases that are ER negative (ER−). Androgen receptor (AR) is expressed in 60-70% of breast tumors, independent of ER status. How androgens and AR regulate breast cancer growth remains largely unknown. We find that AR is enriched in ER−breast tumors that over-express HER2. Through analysis of the AR cistrome and androgen-regulated gene expression in ER−/HER2+ breast cancers we find that AR mediates ligand-dependent activation of Wnt and HER2 signaling pathways through direct transcriptional induction of WNT7B and HER3. Specific targeting of AR, Wnt or HER2 signaling impairs androgen-stimulated tumor cell growth suggesting potential therapeutic approaches for ER−/HER2+ breast cancers.

Programmed death 1 ligand 1 (PD-L1) is an immune regulatory molecule that limits antitumor immune activity. Targeting of PD-L1 and other immune checkpoint proteins has shown therapeutic activity in various tumor types. The expression of PD-L1 and its correlation with response to neoadjuvant chemotherapy in breast cancer has not been studied extensively. Our goal was to assess PD-L1 expression in a cohort of breast cancer patients treated with neoadjuvant chemotherapy. Pre-treatment biopsies from 105 breast cancer patients from Yale New Haven Hospital that subsequently received neoadjuvant chemotherapy were assessed for PD-L1 protein expression by automated quantitative analysis (AQUA) with a rabbit monoclonal antibody (E1L3N) to the cytoplasmic domain of PD-L1. Additionally, tumor-infiltrating lymphocytes (TIL) were assessed on H&E slides.PD-L1 expression was observed in 30% of patients and it was positively associated with hormone-receptor negative and triple-negative status and high levels of TILs. Both TILs and PD-L1 measured in the epithelium or stroma predicted pathologic complete response (pCR) to neoadjuvant chemotherapy in univariate and multivariate analysis. However, since they are strongly associated, TILs and PD-L1 cannot both be included in a significant multivariate model.PD-L1 expression is prevalent in breast cancer, particularly hormone-receptor negative and triple-negative patients, indicating a subset of patients that may benefit from immune therapy. Furthermore, PD-L1 and TILs correlate with pCR and high PD-L1 predicts pCR in multivariate analysis.

Purpose Although tumor infiltrating lymphocytes have been associated with response to neoadjuvant therapy, measurement is typically subjective, semi-quantitative and does not differentiate between subpopulations. Here we describe a quantitative objective method for analyzing lymphocyte subpopulations and assess their predictive value. Methods We develop a quantitative immunofluorescence (QIF) assay to measure stromal expression of CD3, CD8, and CD20 on one slide. We validate this assay by comparison to flow cytometry on tonsil and assess predictive value in breast cancer on a neoadjuvant cohort (n = 95). Then each marker is tested for prediction of pathologic complete response (pCR) compared to pathologist estimation of percentage lymphocyte infiltrate. Results Lymphocyte percentage and CD3, CD8, and CD20 proportions were similar between flow cytometry and QIF on tonsil. Pathologist TIL count predicted pCR (p = 0.043, OR: 4.77[1.05–21.6]) despite fair interobserver reproducibility (κ = 0.393). Stromal AQUA scores for CD3 (p = 0.023, OR: 2.51[1.13–5.57]), CD8 (p = 0.029, OR: 2.00[1.08–3.72]), and CD20 (p = 0.005, OR: 1.80[1.19–2.72]) predicted pCR in univariate analysis. CD20 AQUA score predicted pCR (p = 0.019, OR: 5.37[1.32–21.8]) independently of age, size, nuclear grade, nodal status, ER, PR, HER2, and Ki-67, whereas CD3, CD8, and pathologist estimation did not. Conclusions We have developed and validated an objective, quantitative assay measuring tumor infiltrating lymphocytes in breast cancer. While this work provides analytic validity, future larger studies will be required to prove clinical utility.

Double-stranded DNA ends, often from replication, drive genomic instability, yet their origin in non-replicating cells is unknown. Here we show that transcriptional RNA/DNA hybrids (R-loops) generate DNA ends that underlie stress-induced mutation and amplification. Depleting RNA/DNA hybrids with overproduced RNase HI reduces both genomic changes, indicating RNA/DNA hybrids as intermediates in both. An Mfd requirement and inhibition by translation implicate transcriptional R-loops. R-loops promote instability by generating DNA ends, shown by their dispensability when ends are provided by I-SceI endonuclease. Both R-loops and single-stranded endonuclease TraI are required for end formation, visualized as foci of a fluorescent end-binding protein. The data suggest that R-loops prime replication forks that collapse at single-stranded nicks, producing ends that instigate genomic instability. The results illuminate how DNA ends form in non-replicating cells, identify R-loops as the earliest known mutation/amplification intermediate, and suggest that genomic instability during stress could be targeted to transcribed regions, accelerating adaptation.