Unraveling Vulnerabilities in Endocrine Therapy-Resistant HER2+/ER+ Breast Cancer

Breast tumors overexpressing human epidermal growth factor receptor (HER2) confer intrinsic resistance to endocrine therapy (ET), and patients with HER2/estrogen receptor-positive (HER2+/ER+) breast cancer (BCa) are less responsive to ET than HER2-/ER+. However, real-world evidence reveals that a large subset of patients with HER2+/ER+ receive ET as monotherapy, positioning this treatment pattern as a clinical challenge. In the present study, we developed and characterized 2 in vitro models of ET-resistant (ETR) HER2+/ER+ BCa to identify possible therapeutic vulnerabilities. To mimic ETR to aromatase inhibitors (AIs), we developed 2 long-term estrogen deprivation (LTED) cell lines from BT-474 (BT474) and MDA-MB-361 (MM361). Growth assays, PAM50 subtyping, and genomic and transcriptomic analyses, followed by validation and functional studies, were used to identify targetable differences between ET-responsive parental and ETR-LTED HER2+/ER+ cells. Compared to their parental cells, MM361 LTEDs grew faster, lost ER, and increased HER2 expression, whereas BT474 LTEDs grew slower and maintained ER and HER2 expression. Both LTED variants had reduced responsiveness to fulvestrant. Whole-genome sequencing of aggressive MM361 LTEDs identified mutations in genes encoding transcription factors and chromatin modifiers. Single-cell RNA sequencing demonstrated a shift towards non-luminal phenotypes, and revealed metabolic remodeling of MM361 LTEDs, with upregulated lipid metabolism and ferroptosis-associated antioxidant genes, including GPX4. Combining a GPX4 inhibitor with anti-HER2 agents induced significant cell death in both MM361 and BT474 LTEDs. The BT474 and MM361 AI-resistant models capture distinct phenotypes of HER2+/ER+ BCa and identify altered lipid metabolism and ferroptosis remodeling as vulnerabilities of this type of ETR BCa.

Sponsor Perspectives on the Impact of the COVID-19 Pandemic on Interventional Cancer Clinical Trial Protocols and Data Quality

PURPOSE

The onset of the COVID-19 pandemic created major disruptions in the conduct of cancer clinical trials. In response, regulators and sponsors allowed modifications to traditional trial processes to enable clinical research and care to continue. We systematically evaluated how these mitigation strategies affected data quality and overall trial conduct.

METHODS

This study used surveys and live interviews. Forty-one major industry and National Cancer Institute Network groups (sponsors) overseeing anticancer treatment trials open in the United States from January 2015 to May 2022 were invited to participate. Descriptive statistics were used for survey data summaries. Key themes from interviews were identified.

RESULTS

Twenty sponsors (48.8%; 15 industry and five Network groups) completed the survey; 11/20 (55.0%) participated in interviews. Sponsors predominantly (n = 12; 60.0%) reported large (≥11 trials) portfolios of phase II and/or phase III trials. The proportion of sponsors reporting a moderate (9) or substantial (8) increase in protocol deviations in the initial pandemic wave versus the pre-pandemic period was 89.5% (17/19); the proportion reporting a substantial increased dropped from 42.1% (n = 8/19) in the initial wave to 15.8% (n = 3/19) thereafter. The most commonly adopted mitigation strategies were remote distribution of oral anticancer therapies (70.0%), remote adverse event monitoring (65.0%), and remote consenting (65.0%). Most respondents (15/18; 83.3%) reported that the pandemic had minimal (n = 14) or no impact (n = 1) on overall data integrity.

CONCLUSION

Despite nearly all sponsors observing a temporary increase in protocol deviations, most reported the pandemic had minimal/no impact on overall data integrity. The COVID-19 pandemic accelerated an emerging trend toward greater flexibility in trial conduct, with potential benefits of reduced burden on trial participants and sites and improved patient access to research.

Riluzole Suppresses Growth and Enhances Response to Endocrine Therapy in ER+ Breast Cancer

Background

Resistance to endocrine therapy in estrogen receptor-positive (ER+) breast cancer remains a significant clinical problem. Riluzole is FDA-approved for the treatment of amyotrophic lateral sclerosis. A benzothiazole-based glutamate release inhibitor with several context-dependent mechanism(s) of action, riluzole has shown antitumor activity in multiple malignancies, including melanoma, glioblastoma, and breast cancer. We previously reported that the acquisition of tamoxifen resistance in a cellular model of invasive lobular breast cancer is accompanied by the upregulation of GRM mRNA expression and growth inhibition by riluzole.

Methods

We tested the ability of riluzole to reduce cell growth, alone and in combination with endocrine therapy, in a diverse set of ER+ invasive ductal and lobular breast cancer-derived cell lines, primary breast tumor explant cultures, and the estrogen-independent, ESR1-mutated invasive lobular breast cancer patient-derived xenograft model HCI-013EI.

Results

Single-agent riluzole suppressed the growth of ER+ invasive ductal and lobular breast cancer cell lines in vitro, inducing a histologic subtype-associated cell cycle arrest (G0-G1 for ductal, G2-M for lobular). Riluzole induced apoptosis and ferroptosis and reduced phosphorylation of multiple prosurvival signaling molecules, including Akt/mTOR, CREB, and Fak/Src family kinases. Riluzole, in combination with either fulvestrant or 4-hydroxytamoxifen, additively suppressed ER+ breast cancer cell growth in vitro. Single-agent riluzole significantly inhibited HCI-013EI patient-derived xenograft growth in vivo, and the combination of riluzole plus fulvestrant significantly reduced proliferation in ex vivo primary breast tumor explant cultures.

Conclusion

Riluzole may offer therapeutic benefits in diverse ER+ breast cancers, including lobular breast cancer.

Unraveling Vulnerabilities in Endocrine Therapy-Resistant HER2+/ER+ Breast Cancer

Background

Breast tumors overexpressing human epidermal growth factor receptor (HER2) confer intrinsic resistance to endocrine therapy (ET), and patients with HER2/ estrogen receptor-positive (HER2+/HR+) breast cancer (BCa) are less responsive to ET than HER2-/ER+. However, real-world evidence reveals that a large subset of HER2+/ER+ patients receive ET as monotherapy, positioning this treatment pattern as a clinical challenge. In the present study, we developed and characterized two distinct in vitro models of ET-resistant (ETR) HER2+/ER+ BCa to identify possible therapeutic vulnerabilities.

Methods

To mimic ETR to aromatase inhibitors (AI), we developed two long-term estrogen-deprived (LTED) cell lines from BT-474 (BT474) and MDA-MB-361 (MM361). Growth assays, PAM50 molecular subtyping, genomic and transcriptomic analyses, followed by validation and functional studies, were used to identify targetable differences between ET-responsive parental and ETR-LTED HER2+/ER+ cells.

Results

Compared to their parental cells, MM361 LTEDs grew faster, lost ER, and increased HER2 expression, whereas BT474 LTEDs grew slower and maintained ER and HER2 expression. Both LTED variants had reduced responsiveness to fulvestrant. Whole-genome sequencing of the more aggressive MM361 LTED model system identified exonic mutations in genes encoding transcription factors and chromatin modifiers. Single-cell RNA sequencing demonstrated a shift towards non-luminal phenotypes, and revealed metabolic remodeling of MM361 LTEDs, with upregulated lipid metabolism and antioxidant genes associated with ferroptosis, including GPX4. Combining the GPX4 inhibitor RSL3 with anti-HER2 agents induced significant cell death in both the MM361 and BT474 LTEDs.

Conclusions

The BT474 and MM361 AI-resistant models capture distinct phenotypes of HER2+/ER+ BCa and identify altered lipid metabolism and ferroptosis remodeling as vulnerabilities of this type of ETR BCa.

A Study Design to Harmonize Patient-Reported Outcomes Across Data Sets

PURPOSE

Using patient-reported outcomes (PROs) provides important insights from the patient's perspective and can be valuable to monitor and manage treatment-related adverse events during cancer treatment. Additionally, the digital administration of PROs (electronic PROs [ePROs]) provides real-time updates to clinical care teams on treatment-related symptoms in-between clinic visits. However, given the variability in the methodology and timing of the data collection, using and harmonizing these data across different systems remains challenging. Identifying data elements to capture and operating procedures for harmonization across ePRO tools will expedite efforts to generate relevant and robust data on use of ePRO data in clinical care.

METHODS

Friends of Cancer Research assembled a consortium of project partners from key health care sectors to align on a framework for ePRO data capture across ePRO tools and assessment of the impact of ePRO data capture on patient outcomes.

RESULTS

We identified challenges and opportunities to align ePRO data capture across ePRO tools and aligned on key data elements for assessing the impact of ePRO data capture on patient care and outcomes. Ultimately, we proposed a study protocol to leverage ePRO data for symptom and adverse event management to measure real-world effectiveness of ePRO tool implementation on patient care and outcomes.

CONCLUSION

This work provides considerations for harmonizing ePRO data sets and a common framework to align across multiple ePRO tools to assess the value of ePROs for improving patient outcomes. Future efforts to interpret evidence and evaluate the impact of ePRO tools on patient outcomes will be aided by improved alignment across studies.

ROS is a master regulator of in vitro matriptase activation

Matriptase is a type II transmembrane serine protease that is widely expressed in normal epithelial cells and epithelial cancers. Studies have shown that regulation of matriptase expression and activation becomes deranged in several cancers and is associated with poor disease-free survival. Although the central mechanism of its activation has remained unknown, our lab has previously demonstrated that inflammatory conditions such as intracellular pH decrease strongly induces matriptase activation. In this investigation, we first demonstrate clear matriptase activation following Fulvestrant (ICI) and Tykerb (Lapatinib) treatment in HER2-amplified, estrogen receptor (ER)-positive BT474, MDA-MB-361 and ZR-75-30 or single ER-positive MCF7 cells, respectively. This activation modestly involved Phosphoinositide 3-kinase (PI3K) activation and occurred as quickly as six hours post treatment. We also demonstrate that matriptase activation is not a universal hallmark of stress, with Etoposide treated cells showing a larger degree of matriptase activation than Lapatinib and ICI-treated cells. While etoposide toxicity has been shown to be mediated through reactive oxygen species (ROS) and MAPK/ERK kinase (MEK) activity, MEK activity showed no correlation with matriptase activation. Novelly, we demonstrate that endogenous and exogenous matriptase activation are ROS-mediated in vitro and inhibited by N-acetylcysteine (NAC). Lastly, we demonstrate matriptase-directed NAC treatment results in apoptosis of several breast cancer cell lines either alone or in combination with clinically used therapeutics. These data demonstrate the contribution of ROS-mediated survival, its independence of kinase-mediated survival, and the plausibility of using matriptase activation to indicate the potential success of antioxidant therapy.

OR16-5 Riluzole suppresses growth and enhances response to endocrine therapy in ER+ breast cancer

Approximately 75% of breast cancers are classified as hormone receptor-positive, most of which are estrogen receptor alpha-positive (ER+), which is the primary driver of growth in these tumors. Consequently, endocrine or anti-estrogen therapy is used for treatment. However, despite the benefits of endocrine therapeutics, treatment-resistant relapse is a significant problem that affects 30-50% of patients who initially respond to endocrine therapy. Therefore, studying resistance to endocrine therapy is critical for breast cancer research.We have shown that invasive lobular breast cancer (ILC) cells resistant to the anti-estrogen tamoxifen increase their expression of metabotropic glutamate receptors (GRMs/mGluRs). GRMs are well-known to play important roles in learning and memory in the brain and protect neurons from excitotoxicity (cell death caused by prolonged exposure to neurotransmitters). It is now appreciated that this pro-survival function of GRMs can be highjacked by cancer cells, including breast cancer. Thus, targeting GRM signaling could prove a valuable therapeutic strategy. We chose to target the GRM signaling pathway with the FDA-approved drug Riluzole currently being used to treat amyotrophic lateral sclerosis.In this study, we test the ability of Riluzole to reduce cell growth, alone and in combination with endocrine therapy, in a diverse set of ER+ invasive ductal and lobular breast cancer-derived cell lines, primary breast tumor explant cultures, and the estrogen-independent, ESR1-mutated, ILC-derived patient-derived xenograft model HCI-013EI. In addition to measuring tumor growth rate and size, primary tumors and organs were collected for immunohistochemistry analysis.Riluzole as a single agent suppressed the growth of ER+ invasive ductal and lobular breast cancer cell lines in vitro, inducing differential histologic subtype-associated cell cycle arrest (G0-G1 for ductal, G2-M for lobular). In tamoxifen-resistant ILC cells, Riluzole induced apoptotic and ferroptotic cell death, and inhibited phosphorylation of focal adhesion kinase. Riluzole combined with either fulvestrant or 4-hydroxytamoxifen additively or synergistically suppressed ER+ breast cancer cell growth in vitro. Using proliferating cell nuclear antigen (PCNA) staining as a proxy for cell proliferation, the combination of Riluzole plus Fulvestrant significantly reduced PCNA in a patient-derived explant model (t-test p = 0.013). The in vivo experiment showed reduced tumor size and growth between the control and combination treatments. However, unlike in the in vitro experiment, there was little difference between the single-agent fulvestrant and the combination groups. The observed difference between the in vitro and in vivo study may be attributed to the bioavailability of Riluzole in mice.In conclusion, our results show that Riluzole enhances response to endocrine therapy in ER+ breast cancer.

Presentation: Sunday, June 12, 2022 12:00 p.m. - 12:15 p.m.

Abstract 1014: A framework for research scientists to include patient advocates in cancer research

The inclusion of patient advocates in basic cancer research has emerged as a valuable practice to ensure research is intentional, to support effective communication with broader audiences, and to directly connect researchers with those whom they are striving to help. Despite this value, many researchers do not work with patient advocates. To understand why and build a roadmap for more engagement in the future, we hosted a workshop with patient advocates and research scientists then presented findings and discussed further at an international conference. We acknowledged four main barriers: 1) It is not clear to everyone why patient advocates should be included in research, 2) Researchers are worried about saying the wrong thing, 3) Researchers do not know where to meet patient advocates, and 4) Researchers do not know how to include patient advocates in research. We identified best practices from various organizations and opportunities to overcome these barriers in the short- and long-term. This is the first time a multi-stakeholder group has come together to provide ways to support research scientists with overcoming barriers to regularly working with patient advocates. Ultimately, these relationships will improve cancer research and more quickly accomplish our collective goal of improving lives of those who have been diagnosed with cancer.

Citation Format: Hillary Stires, Igor Bado, Thelma Brown, Martha Carlson, Isaac S. Chan, Gloria V. Echeverria, Andrew J. Ewald, Carla Lloyd, Julia Maues, Steffi Oesterreich, Robert N. Riter, Kelly Shanahan, Alana L. Welm, Josh Newby. A framework for research scientists to include patient advocates in cancer research [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1014.

Abstract 1776: Loss of estrogen receptor alters drug responsiveness and supports a basal-like phenotype in endocrine-resistant HER2+/ER+ breast cancer

At least 50% of human epidermal growth factor 2 (HER2) enriched breast cancer (BC) is estrogen receptor positive (ER+). In clinical trials, patients with HER2+ BC expressing ER respond poorly to neoadjuvant anti-HER2 therapy versus those lacking ER expression. Additionally, combining anti-HER2 with endocrine therapy (ET), like aromatase inhibitor (AI), does not significantly improve pathological complete response in HER2+/ER+ patients. In advanced or de novo HER2+/ER+ metastatic BC (MBC), treatment with ET plus anti-HER2 yields the highest 5-year overall survival. Unfortunately, in the real-world setting outside of clinical trials, just 23% of patients receive this combination, and nearly 40% receive ET alone. The clinical challenge associated with treating advanced HER2+/ER+ BC demands a better understanding of ER signaling and downstream pathways in HER2-driven BC. Our goal is to identify alternative targeted therapies and/or tailor therapeutic combinatorial strategies to treat and/or delay progression of HER2+/ER+ BC. In this study, we established two long-term estrogen (E2) deprived (LTED) HER2+/ER+ cell line models from BT-474 (BT) and MDA-MB-361 (MM) to mimic endocrine therapy resistance (ETR) to AI, and characterized the response of these cell lines to anti-HER2 and other ETs. We also performed whole-genome sequencing (WGS) and single-cell RNA sequencing (scRNAseq) to identify differences between parental and derived ETR-LTEDs. The ER expression was retained in BT-LTEDs but lost in MM-LTEDs as compared to parental cells. Additionally, ER transcriptional activity was confirmed by increased expression of ER-target genes upon E2 stimulation only in BT-LTEDs. However, both LTED variants were less responsive to fulvestrant and showed upregulation of pro-survival AKT signaling. Focusing on the now ER- MM-LTED model, WGS and targeted duplex sequencing identified a significant increase in exonic missense mutations, notably C>T and C>A. Several of the mutated genes encode for transcription and chromatin regulatory factors. scRNAseq analysis showed that MM-LTEDs shift from a luminal- to more basal-like phenotype, with enrichment of genes that regulate immune response and cell motility. Thus, loss of ER expression in MM-LTEDs on the mRNA and protein levels may explain observed intrinsic resistance to fulvestrant and gain of the basal-like phenotype. In summary, we report that our ETR BT- and MM-LTED models capture distinct ER-associated phenotypes of HER2+/ER+ BC. Additional studies are necessary to understand the functional significance of these missense mutations on the development of drug resistance in HER2+/ER+ BC. Ongoing studies are testing pharmacological inhibition of key upregulated genes associated with the basal phenotype to potentially delay disease progression and provide better treatments for ETR HER2+/ER+ BC.

Citation Format: Shaymaa Bahnassy, Hillary Stires, Lu Jin, Stanley Tam, Yasmin J. Dunn, Brendan F. Kohrn, Lawrence A. Loeb, Manasi Balachandran, Mircea Podar, Matthew D. McCoy, Robert A. Beckman, Rebecca B. Riggins. Loss of estrogen receptor alters drug responsiveness and supports a basal-like phenotype in endocrine-resistant HER2+/ER+ breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1776.

Abstract 2461: Integrated lifetime and spectral phasor imaging of biomarker expression and metabolism in hormone receptor positive breast cancer models

In HR+ (hormone receptor positive) breast cancer, endocrine therapies that directly antagonize estrogen receptor or reduce synthesis of its ligand can be highly effective, but endocrine-resistance occurs frequently. Metabolic dysregulation is a mechanistic driver of endocrine-resistant HR+ breast cancer, but most existing methods cannot be multiplexed with assays for biomarker expression. Spectral phasor imaging of multiplex immunofluorescence (mIF) staining for expression of hormone receptors and other biomarkers combined with phasor lifetime analysis of NADH to quantify metabolic state will provide integrated spatial maps of metabolism and biomarker expression in endocrine-resistant HR breast cancer. We used the HCI-013 (013) and HCI-013EI (013EI) patient-derived xenograft (PDX) system, derived from a HR+, invasive lobular metastatic breast cancer which harbors the Y537S ESR1 mutation. Tumors were stained with a multiplex immunofluorescence (mIF) panel for pan-cytokeratin, ER, PR, HER2, and Ki67, detected by spectrally separate OPAL dyes. Hyperspectral phasor fluorescence spectra were obtained using successive single photon excitation at 488 nm, 561 nm and 640 nm and using multiphoton excitation at 1024 nm. Single photon excitation excites specific dyes, and multiphoton excites the entire panel of dyes simultaneously. The emission was collected using a Zeiss 880 laser scanning microscope equipped with a 32 channel spectral detector. Phasor coordinates of each component were resolved into fractional intensities of the five genes. In the same tissues and sections, phasor fluorescence lifetime imaging (FLIM) of NADH was used to quantify metabolic heterogeneity. NADH is present in two forms: free and protein-bound NADH. They have different fluorescence lifetimes and the ratio of these two species are correlated with NAD+/NADH ratio. Free NADH is associated with increased glycolysis. We observed greater metabolic heterogeneity in 013EI PDX samples, with similar levels of free NADH (glycolysis) at the tumor border, but significantly increased bound NADH (oxidative phosphorylation) in the tumor core. Spectral phasor data show differential expression of PR and PanCK (for 640 nm excitation), and HER2 and ERalpha (for 561 nm excitation) in the edge and center of cancer in 013 and 013EI variants. Our results show how a combination of spectral phasor and phasor-FLIM can be used to define metabolic changes in endocrine-resistant, HR+ PDX models and correlate them with biomarker expression. Ongoing work is quantitatively mapping these measurements at single-pixel resolution, and applying this imaging workflow to RNAscope in situ hybridization assays for gene expression. Combining multiphoton spectral (RNAscope) and FLIM (NADH) will allow pixelwise correlation of the gene expression and metabolic changes.

Citation Format: Belen Torrado, Alexander Vallmitjana, Ayodeji Olukoya, Shaymaa Bahnassy, Hillary Stires, Aaron Rozeboom, Rebecca B. Riggins, Suman Ranjit. Integrated lifetime and spectral phasor imaging of biomarker expression and metabolism in hormone receptor positive breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2461.

Breakthrough Therapy Designation Criteria Identify Drugs that Improve Clinical Outcomes for Patients: A Case for More Streamlined Coverage of Promising Therapies

Breakthrough therapy designation (BTD) is a valuable tool for expediting approval of promising therapies in oncology. Expediting drug development and review is time and resource intensive, so it is imperative to assess the performance of BTD and determine whether the criteria identify promising drugs that lead to improved outcomes for patients. This perspective provides a comparison of clinical outcomes data and National Comprehensive Cancer Network (NCCN) clinical guidelines for drugs indicated to treat non-small cell lung cancer (NSCLC) approved with BTD or without BTD between January 2013 and October 2021. Across the 31 approvals supported by data from randomized controlled trials, with the primary or co-primary endpoints of progression-free survival and/or overall survival, BTD drugs reduced the risk of death by a median of 31% and progression by a median of 48%, while drugs never receiving BTD ("Never BTD") reduced the risk of death and progression by a median of 15% and 41.9%, respectively. More BTD drugs received a NCCN recommendation in the highest category of evidence (Category 1) than Never BTD drugs, and a greater proportion of BTD drugs were considered "preferred" compared to Never BTD drugs. In the context of this improved value, we provide considerations for establishing an expedited pathway for coverage decisions on BTD drugs to support timely access for patients. These results suggest the qualifying criteria for BTD identify drugs that improve outcomes for patients with cancer, and thus, may benefit from mechanisms that expedite processes to ensure timely coverage decisions and access for patients.

OUP accepted manuscript

Background

Homologous recombination deficiency (HRD) is a phenotype that is characterized by the inability of a cell to effectively repair DNA double-strand breaks using the homologous recombination repair (HRR) pathway. Loss-of-function genes involved in this pathway can sensitize tumors to poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibitors and platinum-based chemotherapy, which target the destruction of cancer cells by working in concert with HRD through synthetic lethality. However, to identify patients with these tumors, it is vital to understand how to best measure homologous repair (HR) status and to characterize the level of alignment in these measurements across different diagnostic platforms. A key current challenge is that there is no standardized method to define, measure, and report HR status using diagnostics in the clinical setting.

Methods

Friends of Cancer Research convened a consortium of project partners from key healthcare sectors to address concerns about the lack of consistency in the way HRD is defined and methods for measuring HR status.

Results

This publication provides findings from the group’s discussions that identified opportunities to align the definition of HRD and the parameters that contribute to the determination of HR status. The consortium proposed recommendations and best practices to benefit the broader cancer community.

Conclusion

Overall, this publication provides additional perspectives for scientist, physician, laboratory, and patient communities to contextualize the definition of HRD and various platforms that are used to measure HRD in tumors.

Weight Gain and Related Comorbidities Following Antiretroviral Initiation in the 2000s: A Systematic Literature Review

Antiretroviral therapies (ARTs) benefit millions with human immunodeficiency virus. However, concerns about subsequent weight gain and related metabolic complications have emerged. Early ARTs are associated with adipose tissue changes. While newer ARTs may have fewer adipose alterations, it is unclear whether they lead to increased weight gain. A systematic literature review was performed to describe current published literature describing the use of newer ARTs, weight gain, and related comorbidities. Titles and abstracts were screened, focusing on studies that examined ART initiation and subsequent weight gain; publications were then ranked based on publication type, methodology, and comorbidities, emphasizing US studies with large patient cohorts. This yielded a comprehensive review of the 50 publications on weight gain and a range of related comorbidities, including diabetes and hypertension. Most of the studies describing weight gain found the most significant gains during the first year after initiating ART. Overall, patients gained ∼5 kg 18-96 months after initiating ART. Many of the studies reported altered weight-related comorbidities, including increased risk of diabetes and hypertension. Despite an expectation that newer ARTs may be safer, a review of the literature suggests that contemporary ART use is associated with pronounced weight gain and related comorbidities. Future studies should define and quantify the direct role of newer ARTs in weight gain and related comorbidities, as well as clarify the role of specific drug classes in metabolic disturbance, to improve intervention strategies.

SAT-119 Targeting Glutamate Metabolism and Signaling in ER+, Endocrine Therapy-Resistant Breast Cancer

Estrogen receptor-positive (ER+) breast cancer is the most commonly diagnosed form of this malignancy. Aromatase inhibitors and selective estrogen receptor modulators or degraders (SERMS, SERDs) can be highly effective in treating ER+ breast cancer, but de novo and acquired resistance to these interventions is a persistent clinical problem. Endocrine therapy resistant breast cancer cells rewire their metabolism to support cellular demands associated with rapid proliferation and/or increased invasion and metastasis. An important feature of this metabolic flexibility is conversion of glutamine to glutamate, an amino acid integral to protection of cells from oxidative stress. Consistent with this, we show multiple cellular models of ER+, endocrine resistant breast cancer cells markedly increase glutamate release and upregulate expression of essential glutamine/glutamate metabolic enzymes and transporters, including the glutamate/cystine antiporter xCT, glutamate dehydrogenase (GLUD1/2), and/or the glutamine importer SLC1A5. Riluzole (RIL) is FDA-approved for the treatment of amyotrophic lateral sclerosis (ALS), and has several proposed mechanisms of action, including suppression of glutamate release and increased glutamate uptake. We show ER+, endocrine responsive and resistant breast cancer cells are growth-inhibited by RIL. This is due to an increase in cell death, particularly in endocrine resistant breast cancer cells, and cell cycle arrest. Interestingly, histologic subtype confers a different cell cycle arrest profile, with invasive ductal cancer (IDC) models arresting in G1 but invasive lobular cancer (ILC) models arresting in G2/M. Isobologram analysis of RIL plus SERMs or SERDs shows additive-to-synergistic activity in a subset of ER+ cell line models, and preliminary studies show combination activity in patient-derived explants (PDEs). Mechanistically, we tested whether signaling through metabotropic glutamate receptors (mGluRs, GRMs) and/or cystine import contribute to RIL’s growth-inhibitory phenotype. Antagonists of mGluRs/GRMs don’t phenocopy the effects of RIL, suggesting extracellular glutamate signaling through these receptors is not a key mechanism. Rescue experiments with β-mercaptoethanol to promote cystine uptake through transporters other than xCT show partial reversal of RIL-mediated cell cycle arrest in some cells, suggesting xCT may contribute to RIL-induced growth inhibition. In summary, we show RIL may be a viable addition to endocrine therapy in ER+ breast cancer. Ongoing studies will test additional mechanism(s) by which RIL may attenuate the growth of ER+ breast cancer models in vitro, including inhibition of protein kinase C and casein kinase 1 delta. We are further testing RIL efficacy alone and in combination with a SERD in primary tumors and lung metastases in a ER+ patient-derived xenograft (PDX) model.

Integrated molecular analysis of Tamoxifen-resistant invasive lobular breast cancer cells identifies MAPK and GRM/mGluR signaling as therapeutic vulnerabilities

Invasive lobular breast cancer (ILC) is an understudied malignancy with distinct clinical, pathological, and molecular features that distinguish it from the more common invasive ductal carcinoma (IDC). Mounting evidence suggests that estrogen receptor-alpha positive (ER+) ILC has a poor response to Tamoxifen (TAM), but the mechanistic drivers of this are undefined. In the current work, we comprehensively characterize the SUM44/LCCTam ILC cell model system through integrated analysis of gene expression, copy number, and mutation, with the goal of identifying actionable alterations relevant to clinical ILC that can be co-targeted along with ER to improve treatment outcomes. We show that TAM has several distinct effects on the transcriptome of LCCTam cells, that this resistant cell model has acquired copy number alterations and mutations that impinge on MAPK and metabotropic glutamate receptor (GRM/mGluR) signaling networks, and that pharmacological inhibition of either improves or restores the growth-inhibitory actions of endocrine therapy.

Abstract 3605: The role of androgen receptor in invasive lobular breast carcinoma

The leading problem for women with estrogen receptor α (ER) breast cancer – approximately 70% of all breast cancers – is that while the majority of tumors initially respond to anti-estrogen treatment including Tamoxifen and aromatase inhibitors, they will develop endocrine resistance. A histological subset of breast cancer called invasive lobular carcinoma (ILC) accounts for 15% of all breast cancer cases and approximately 90% of ILC are ER-positive. Despite clinical markers suggesting a better prognosis for ILC compared to the more common invasive ductal carcinoma (IDC), recent data suggests women with ILC develop Tamoxifen resistance at a higher rate than IDC. New strategies for treating hormone refractory tumors are needed that not only overcome anti-estrogen resistance, but also present a more tolerable side effect profile and have fewer dose-limiting toxicities than adjuvant chemotherapy. The majority of ER-positive breast cancers also express androgen receptor (AR) and while AR presence in breast cancer is controversial, increased expression of AR leads to Tamoxifen resistance in IDC cell lines. Since ILC has more AR expression than IDC, the role of AR in ILC was studied by treating cells with the non-aromatizable androgen dihydrotestosterone (DHT) and the synthetic androgen R1881 as well as the anti-androgen Enzalutamide. We have previously begun to characterize a Tamoxifen resistant variant of the ILC cell line Sum44PE termed LCCTam cells. In both Sum44PE and LCCTam cells, AR protein expression increases in response to androgens, an action that is blocked by Enzalutamide. Interestingly, androgens do not promote growth in ILC cells, but Enzalutamide is still able to inhibit growth. These results suggest Enzalutamide may be an effective alternative therapy for women with ILC. Future studies will focus on whether regulation of nuclear receptor co-factors influences differences in AR signaling in ILC.

Citation Format: Hillary Stires, Rebecca B. Riggins. The role of androgen receptor in invasive lobular breast carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3605. doi:10.1158/1538-7445.AM2017-3605

Pre-clinical analysis of the CDK4/6 inhibitor palbociclib in HER2-positive breast cancer

e12520

Background: There has been substantial progress in treatment of metastatic HER2+ breast cancer, unfortunately, treatment progression of the disease is universal. Palbociclib is an oral cyclin-dependent kinase (CDK) 4/6 inhibitor that is FDA approved in combination with endocrine therapy for treatment of patients with ER+ metastatic breast cancer. Here we present pre-clinical studies in HER2+ breast cancer cell lines investigating whether addition of palbociclib to the combination of trastuzumab and pertuzumab (TP) is an effective therapy, and whether we could identify predictive biomarkers for palbociclib in this setting. Methods: Crystal violet assays to measure growth of BT-474 (HER2+, ER+), SKBr3 (HER2+, ER-) and MDA-MB-361 (HER2+, ER+ but resistant to TP) were performed in the presence and absence of TP (5 µg/ml each) with increasing concentrations of palbociclib (25-500 µg/ml). Western blots were performed in the presence and absence of TP with and without palbociclib to demonstrate efficacy of TP (blocking phosphorylation of HER2), palbociclib (blocking phosphorylation of Rb), and expression of NIMA-related kinase 2 (NEK2), an established downstream target of CDK4 in HER2+ breast cancer cells. Results: We found growth inhibition in response to palbociclib as single agent in a dose-dependent manner in BT-474, SKBr3, and MDA-MB-361 cells (P < 0.05). Treatment with TP prevented growth in BT-474 and SKBr3 cells to such a great extent that an additive effect between TP and palbociclib was not detectable. However, treatment with palbociclib maintained a dose-dependent decrease in growth in the presence of TP in MDA-MB-361 cells (P < 0.05). Western blots showed decreased expression of pHER2 in response to TP in BT-474 and SKBr3, but not in MDA-MB-361. Treatment with palbociclib decreased pRB in BT474, SKBr3, and MDA-MB-361 with or without TP. NEK2 expression, however, was not affected in any of these cell lines. Conclusions: Palbociclib has an inhibitory effect in resistant and non-resistant HER2-positive cell lines suggesting palbociclib represents an alternate targeting pathway for growth inhibition. Our initial work did not show reliable biomarkers to predict palbociclib effects.

The Arcuate Estrogen-Regulated Transcriptome: Estrogen Response Element-Dependent and -Independent Signaling of ERα in Female Mice

To influence energy homeostasis and reproduction, 17β-estradiol (E2) controls the arcuate nucleus (ARC) through multiple receptor-mediated mechanisms, but primarily via estrogen receptor (ER) α, which signals through both estrogen response element (ERE)-dependent and -independent mechanisms. To determine ERα-mediated, ERE-dependent, and ERE-independent E2 signaling in the ARC, we examined the differential regulation of the mouse arcuate transcriptome by E2 using three mice genotypes: (1) wild-type, (2) ERα knock-in/knockout (ERE-independent mechanisms), and (3) total ERα knockout (ERα-independent mechanisms). Females were ovariectomized and injected with oil or E2, and RNA sequencing on the ARC was used to identify E2-regulated genes in each genotype. Our results show that E2 regulates numerous genes involved in cell signaling, cytoskeleton structure, inflammation, neurotransmission, neuropeptide production, and transcription. Furthermore, ERE-independent signaling regulates ARC genes expressed in kisspeptin neurons and transcription factors that control the hypothalamic/pituitary/gonadal axis. Interestingly, a few genes involved in mitochondrial oxidative respiration were regulated by E2 through ERα-independent signaling. A comparison within oil- and E2-treated females across the three genotypes suggests that genes involved in cell growth and proliferation, extracellular matrices, neuropeptides, receptors, and transcription are differentially expressed across the genotypes. Comparing with previously published chromatin immunoprecipitation sequencing analysis, we found that ERE-independent regulation in the ARC is mainly mediated by tethering of ERα, which is consistent with previous findings. We conclude that the mouse arcuate estrogen-regulated transcriptome is regulated by multiple receptor-mediated mechanisms to modulate the central control of energy homeostasis and reproduction, including novel E2-responsive pathways.

Peroral Estradiol Is Sufficient to Induce Carcinogen-Induced Mammary Tumorigenesis in Ovariectomized Rats without Progesterone

A role for estrogens in breast cancer is widely accepted, however, recent evidence highlights that timing and exposure levels are important in determining whether they elicit harmful versus beneficial effects. The rat chemical carcinogen model has been widely used to study the effects of estrogens but conclusions on the levels that lead to tumor development and an absolute requirement for progesterone (P4) are lacking. A newer method of hormone administration mixes hormones with nut butter for peroral consumption allowing for a less stressful method of long-term administration with lower spikes in serum estradiol (E2) levels. The present study was designed to determine if estrogens alone at a physiological dose can drive carcinogen-induced tumors in ovariectomized (OVX) rats or if P4 is also required using this method of hormone administration. Short-term studies were conducted to determine the dose of estrogen (E) that would lead to increased uterine weight following OVX. Subsequently, rats were OVX on postnatal day (PND) 40 then treated daily with E (600 μg/kg/day), P4 (15 mg/kg/day), or the combination. On PND 50, all rats were injected with nitrosomethylurea to induce mammary tumors. Uterine weights, body weights, and serum E2 levels were measured to demonstrate the efficacy of the method for increasing E2 levels during long-term treatment. After 26 weeks, tumor incidence was similar in Sham, E, and E + P4 animals indicating that E was sufficient to induce tumorigenesis when hormone levels were normalized by this method. This study demonstrates peroral administration can be used in long-term studies to elucidate relationships between different types and levels of steroid hormones.

Abstract 785: The prepubertal mammary gland transcriptome suggests a role for the immune system in hormone-independent breast cancer

Identifying signaling pathways involved in mammary gland development has contributed to our understanding of breast cancer. While growth of the gland is isometric between birth and puberty, ductal expansion is significant and morphological changes such as terminal end bud formation occur during this developmental window. While estrogen receptor alpha (ERá) and progesterone receptor (PR) expression are evident during this time, pre-pubertal levels of free estradiol are low and growth is independent of ovarian hormones. Basal-like breast cancers represent a subset of breast cancers (10-15% of all women with breast cancer) that often lack ERá, PR and HER2 (i.e. triple negative), are ovarian hormone independent, and have a worse prognosis than other tumor subtypes. Animal models for basal-like breast cancer are limited. Therefore identifying gene changes during prepubertal mammary gland development may give insight into the mechanisms that drive these breast cancers. Offspring from individual Sprague Dawley dams were sacrificed on postnatal days (PND) 2, 10 and 20 (n = 5 to 6 for each PND) and the fourth inguinal glands were removed. RNA was isolated and sequenced by RNASeq using 25 million paired end reads. Bioinformatics analysis utilizing TopHat, Bowtie2, and CummeRbund revealed &gt;7000 genes that changed during this time (alpha = 0.05). Analysis by DAVID/KEGG and Ingenuity Pathway Analysis demonstrated differences in immune pathways over time whereby immune genes increased from PND 2 to 10 to 20. Specifically, T Cell Receptor Signaling and B Cell Development were two of the most affected pathways. These results are interesting as recent studies have indicated that the immune system may influence basal-like breast cancers. Molecular signatures defining subtypes of basal-like breast cancer have been described and include basal-like immunosuppressed (BLIS) and basal-like immune activated (BLIA). A better understanding of the role of the immune system in prepubertal mammary gland development may help guide treatment strategies for hormone independent breast cancers.

Citation Format: Hillary Stires, Catina Crismale-Gann, William J. Belden, Wendie S. Cohick. The prepubertal mammary gland transcriptome suggests a role for the immune system in hormone-independent breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 785.

Tumor Phenotype and Gene Expression During Early Mammary Tumor Development in Offspring Exposed to Alcohol In Utero

BACKGROUND

Alcohol exposure in utero increases susceptibility to carcinogen-induced mammary tumorigenesis in adult offspring and causes tumors with a more malignant phenotype. This study was conducted to identify changes early in tumor development that might lead to this outcome.

METHODS

Pregnant Sprague-Dawley rats were fed a liquid diet containing 6.7% ethanol (alcohol), an isocaloric liquid diet without alcohol (pair-fed), or rat chow ad libitum (ad lib) from gestation day 7 until parturition. At birth, female progeny were cross-fostered to control dams. Pups were weaned at postnatal day (PND) 21 and fed rat chow ad libitum for the remainder of the experiment. Female offspring were administered N-nitroso-N-methylurea (NMU; 50 mg/kg body weight) on PND 50. Mammary glands were palpated weekly, and offspring were euthanized at 16 weeks post-NMU injection.

RESULTS

At 16 weeks post-NMU, tumor multiplicity was greater in alcohol-exposed offspring compared with control groups. Estrogen receptor-α (ER) mRNA expression was decreased in tumors from alcohol-exposed offspring, and these animals developed more ER-negative tumors relative to the pair-fed group. Alcohol-exposed offspring also tended to develop more progesterone receptor (PR)-positive tumors. All tumors were HER2-negative. PR positivity was associated with higher Ki67 expression, suggesting that PR-positive tumors were more proliferative. Tumors from alcohol-exposed animals exhibited increased mRNA expression of the insulin-like growth factor (IGF) family members IGF-II and IGFBP-5. IGF-II and DNA methyltransferase mRNA tended to be greater in the normal contralateral mammary glands of these animals.

CONCLUSIONS

These data indicate that alcohol exposure in utero may shift NMU-induced tumor development toward a more aggressive phenotype and that alterations in IGF-II expression may contribute to these changes. Additional studies should be aimed at epigenetic mechanisms that underlie IGF-II expression to further delineate how this gene is altered in mammary glands of adults exposed to alcohol in utero.

Endogenous IGFBP-3 Mediates Intrinsic Apoptosis Through Modulation of Nur77 Phosphorylation and Nuclear Export

In nontransformed bovine mammary epithelial cells, the intrinsic apoptosis inducer anisomycin (ANS) induces IGFBP-3 expression and nuclear localization and knockdown of IGFBP-3 attenuates ANS-induced apoptosis. Others have shown in prostate cancer cells that exogenous IGFBP-3 induces apoptosis by facilitating nuclear export of the orphan nuclear receptor Nur77 and its binding partner, retinoid X receptor-α (RXRα). The goal of the present work was to determine whether endogenous IGFBP-3 plays a role in ANS-induced apoptosis by facilitating nuclear transport of Nur77 and/or RXRα in nontransformed cells. Knockdown of Nur77 with siRNA decreased ANS-induced cleavage of caspase-3 and -7 and their downstream target, PARP, indicating a role for Nur77 in ANS-induced apoptosis. In cells transfected with IGFBP-3, IGFBP-3 associated with RXRα but not Nur77 under basal conditions, however, IGFBP-3 co-precipitated with phosphorylated forms of both proteins in ANS-treated cells. Indirect immunofluorescence and cell fractionation techniques showed that ANS induced phosphorylation and transport of Nur77 from the nucleus to the cytoplasm and these effects were attenuated by knockdown of IGFBP-3. These data suggest that endogenous IGFBP-3 plays a role in intrinsic apoptosis by facilitating phosphorylation and nuclear export of Nur77 to the cytoplasm where it exerts its apoptotic effect. Whether this mechanism involves a physical association between endogenous IGFBP-3 and Nur77 or RXRα remains to be determined.

Abstract 2724: NMU induction of mammary tumors in ovariectomized rats administered peroral estrogen and progesterone

Mammary tumors induced by carcinogens such as N-nitroso-N-methylurea (NMU) are thought to be estrogen dependent since ovariectomy (OVX) or treatment with tamoxifen or aromatase inhibitors inhibits mammary tumor development. However, whether NMU-induced tumor formation can be restored in OVX animals with estradiol (E2) and/or progesterone (P4) administration is unclear. Common methods of hormone administration such as pellet implants, injections or gavage feeding can lead to supraphysiological levels of hormone or unwarranted stress for use in long term tumor studies. To circumvent these problems, we administered hormones daily in peanut butter to OVX Sprague-Dawley rats. Short-term (10 day) pilot studies were conducted to determine the dose of E2 that would decrease body weights and increase uterine weights of OVX animals relative to sham controls. An initial pilot using 150 μg/kg E2 for 10 days led to decreased body weight gain in OVX animals but was unable to restore uterine weights. A second pilot analyzed a dose of 300 μg/kg or 600 μg/kg E2. Body weights were repressed in both groups relative to OVX, but only the 600 μg/kg dose was able to restore uterine weights. Therefore the 600 μg/kg dose was used to test whether hormones fed in peanut butter could drive tumor development. Following surgery on PND 40, rats received daily treatments in peanut butter throughout the study. Rats that were OVX were divided into four treatment groups (n = 8): 1) E2; 2) P4 (15 mg/kg); 3) E2 + P4; and 4) vehicle, with a fifth group given vehicle after sham surgery (n = 8) as a positive control. On PND 50, all animals received a single I.P. injection of 50 mg/kg NMU to induce mammary tumors. Rats were weighed and palpated biweekly. Blood was collected via tail vein at 4, 8 and 12 weeks following NMU administration 2 to 4 hours after hormone feeding. Analysis of serum E2 indicated that levels were elevated and not supraphysiological. Body weights of E2 groups with or without P4 were similar to sham body weights while the P4 group had body weights similar to those of untreated OVX rats. Mammary tumors were first observed between 6 and 7 weeks post NMU-injection in sham, E2 + P4 and E2 animals. At 18 weeks, 62.5, 37.5, and 25% of rats presented with tumors and total tumors per group were 8, 3 and 3 in sham, E2 + P4 and E2 groups, respectively. One tumor was observed in an OVX + vehicle rat at 8.5 weeks while no tumors were observed in the P4 group. Collectively, these studies indicate that administering hormones perorally in peanut butter restores body weights and uterine weights of OVX animals and allows for tumor formation in response to NMU. The lower tumor incidence in OVX animals receiving hormones suggests that additional factors may be necessary to fully restore NMU-induced tumors.

Citation Format: Hillary Stires, Mariana D. Saboya, Samantha P. Globerman, Wendie S. Cohick. NMU induction of mammary tumors in ovariectomized rats administered peroral estrogen and progesterone. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2724. doi:10.1158/1538-7445.AM2015-2724

Fetal alcohol exposure and mammary tumorigenesis in offspring: role of the estrogen and insulin-like growth factor systems

Fetal alcohol spectrum disorders affect a significant number of live births each year, indicating that alcohol consumption during pregnancy is an important public health issue. Environmental exposures and lifestyle choices during pregnancy may affect the offspring's risk of disease in adulthood, leading to the idea that a woman's risk of breast cancer may be pre-programmed prior to birth. Exposure of pregnant rats to alcohol increases tumorigenesis in the adult offspring in response to mammary carcinogens. The estrogen and insulin-like growth factor (IGF-I) axes occupy central roles in normal mammary gland development and breast cancer. 17-β estradiol (E2) and IGF-I synergize to regulate formation of terminal end buds and ductal elongation during pubertal development. The intracellular signaling pathways mediated by the estrogen and IGF-I receptors cross-talk at multiple levels through both genomic and non-genomic mechanisms. Several components of the E2 and IGF-I systems are altered in early development in rat offspring exposed to alcohol in utero, therefore, these changes may play a role in the enhanced susceptibility to mammary carcinogens observed in adulthood. Alcohol exposure in utero induces a number of epigenetic alterations in non-mammary tissues in the offspring and other adverse in utero exposures induce epigenetic modifications in the mammary gland. Future studies will determine if fetal alcohol exposure can induce epigenetic modifications in genes that regulate E2/IGF action at key phases of mammary development, ultimately leading to changes in susceptibility to carcinogens.

Abstract 3595: Effects of fetal alcohol exposure on tumor development and gene expression in rats

Fetal alcohol exposure increases susceptibility to carcinogen induced mammary tumors in adult rats. These animals exhibit hyperproliferative mammary glands pre-pubertally, suggesting that early changes are taking place in the mammary gland. To determine the molecular mechanisms that underlie these effects, pregnant Sprague Dawley rats were fed a liquid diet containing 6.7% ethanol, pair-fed an isocaloric liquid diet, or fed rat chow ad libitum from days 11 to 21 of gestation. Pups were cross-fostered to ad libitum-fed control dams at birth. At postnatal day 50, offspring were injected with NMU to induce mammary tumors and tissues were collected at 16 weeks post-injection, the time-point when approximately half of all animals exhibited tumors in our previous study. Significantly more tumors were observed in the fetal alcohol group compared to control groups. Histological analysis indicated that fetal alcohol exposed rats developed more adenocarcinomas. Interestingly, mammary tissue from these animals exhibited more adenosis compared to controls. Since we have previously observed changes in the estradiol/estrogen receptor (ER) system and a recent study found that epithelial to mesenchymal transition (EMT) genes are altered in the rat fetal alcohol NMU model, a custom PCR array was designed to examine expression of genes involved in EMT, estradiol/ER signaling, and tumorigenesis in tumor samples and mammary tissue collected from contralateral tumor-free glands. Mammary glands from fetal alcohol animals had increased expression of EMT genes compared to pair-fed controls. Snail and Twist, two genes whose increased expression is considered the hallmark of EMT, exhibited the greatest changes. Previously, we found that mammary tumors collected at 23 weeks post-NMU injection were more ER negative in fetal alcohol animals. Therefore, we were interested in determining if a similar change was evident at 16 weeks post-injection. Immunohistochemical (IHC) analysis indicated that at this earlier time-point, mammary tumors from the fetal alcohol group were not more ER negative compared to controls. To determine if the ER is functional, IHC analysis was performed to determine the expression of progesterone receptor (PR), a downstream target of ER. The majority of tumors from each treatment group were PR negative. To complete the receptor status profile, IHC was also performed for HER2. The majority of all tumors across the three treatment groups were HER2 negative. These data indicate that fetal alcohol exposure alters expression of several genes in the mammary gland, which may be involved in the molecular mechanisms underlying the increased risk in mammary tumorigenesis.

Citation Format: Catina Crismale-Gann, Tiffany A. Polanco, Hillary Stires, Wendie S. Cohick. Effects of fetal alcohol exposure on tumor development and gene expression in rats. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3595. doi:10.1158/1538-7445.AM2013-3595