Hormone Negative Breast Cancer Research Articles

Abstract PO4-14-01: Synergistic Activity of CDK8/19 Inhibitor RVU120 and MEK Inhibitors in Hormone-Negative Breast Cancer: Implications for Targeted Therapy

Abstract Breast cancer (BC) is a complex disease with distinct subtypes, including triple-negative breast cancer (TNBC), which lacks targeted therapies. CDK8 and CDK19, components of the mediator complex involved in transcriptional regulation, have emerged as potential therapeutic targets in BC. Transcriptomic analysis revealed that elevated CDK8 expression was associated with poor prognosis across all BC subtypes. Furthermore, previous studies demonstrated that sensitivity to CDK8/CDK19 inhibition correlated with high STAT3 phosphorylation and enrichment of TNF/NF-kB and STAT target genes in responder cells. In this study, we evaluated the responsiveness of TNBC cell lines to RVU120, a highly selective and potent CDK8/CDK19 inhibitor currently undergoing clinical trials for acute myeloid leukemia (AML), high-risk myelodysplastic syndrome (HR-MDS), and solid tumors. Notably, the sensitivity of TNBC cell lines to RVU120 varied depending on the culture conditions, with the presence of epidermal growth factor (EGF) identified as a major determinant of response variability. Considering the role of EGFR in activating downstream signaling pathways, including MAPK and STAT, and previous observations of synergy between small molecule CDK8 inhibitors and MEK inhibitors in neuroblastoma, we investigated MEK inhibitors as potential combination partners in hormone-negative BC. Among the 15 tested BC cell lines, a synergy between CDK8/CDK19 inhibitors and MEK inhibitors was observed in 5 cell lines, antagonism in another 5 cell lines, and no synergy in the remaining 5 cell lines, based on the analysis with Combenefit software (Loewe additivity model). Importantly, cell lines where synergy of the combination therapy has been observed, exhibited EGFR amplification and markers of activated RAS pathway. This pattern of response was consistent across different MEK and MEK/RAF inhibitors, including selumetinib, trametinib, and avutometinib. These findings highlight the synergistic potential of combining RVU120 with MEK inhibitors in hormone-negative BC, particularly in TNBC with EGFR amplification and an active RAS pathway. Ongoing studies involving RNAseq analysis and organoid screening aim to further elucidate the underlying mechanisms and confirm the efficacy of this combination therapy. Furthermore, in vivo efficacy experiments are necessary to validate in vitro activity of both compounds. Successful development of this therapeutic concept relies on the validation and implementation of selected partner drugs targeting RAS pathway, as well as the identification of suitable biomarkers such as EGFRamp or RAS-score. Promising findings of this study provide a rationale for exploring the combination of CDK8/CDK19 inhibitor RVU120 and MEK inhibitors as a potential targeted therapy strategy for hormone-negative BC. Citation Format: Urszula Pakulska, Adrianna Moszynska, Justyna Martyka, Jerzy Woznicki, Elzbieta Adamczyk, Marta Obacz, Kinga Keska Izworska, Katarzyna Wiklik, Agata Stachowicz, Hendrik Nogai, Milena Mazan, Tomasz Rzymski. Synergistic Activity of CDK8/19 Inhibitor RVU120 and MEK Inhibitors in Hormone-Negative Breast Cancer: Implications for Targeted Therapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-14-01.

BMI and mortality in hormone-negative breast cancer: A PLCO trial subgroup analysis.

e12544 Background: Body Mass Index (BMI) is a significant prognostic factor in the survival of patients with hormone receptor-positive breast cancer (BC).[1-2] However, the relationship between BMI and survival is not well-established in hormone receptor-negative (HR-) breast tumors. [3] Emerging data is mixed: some studies show that BMI does not impact outcomes in HR- tumors [4], while others reveal worse survival in patients with elevated BMI.[5] In this study, our objective was to corroborate recent evidence about the relationship between BMI and mortality in hormone-negative breast cancer. Methods: We used the PLCO cancer screening trial, a publicly available database containing information about 155,000 participants enrolled in the United States between 1993 and 2001. Data were collected on cancer mortality through 2018 (median follow-up of 19.2 years post enrollment). The methodology of the PLCO trial has been described previously.[6] All female patients with a diagnosis of HR- BC diagnoses were selected for data retrieval, including HR-/HER2+ and HR-/HER2- tumors. Patients with equivocal receptor status were excluded. We used multivariate Cox regression to analyze mortality by BMI category, after adjusting for all significant variables at the bivariate level ( p <0.25). Results: 348 women with confirmed HR- BC at the time of study participation were included. Mean age was 69 years old, and 62 patients (17.8%) passed away due to breast cancer during study enrollment or follow-up. Patients who were of normal weight (BMI 25-<30) at age of trial enrollment were not significantly more likely to survive compared to overweight or obese patients (Hazard Ratio 1.274, p= 0.623). Conclusions: Our results show no significant relationship between BMI and mortality in patients with HR- BC tumors. This finding adds to the growing literature about weight status in hormone receptor-negative tumors. Our data suggests that the mechanism of tumor progression in HR- breast tumors is unlikely to involve signaling mechanisms in adipocytes. Clinical trial information: NCT00002540 , NCT01696968 , NCT01696981 , NCT01696994 . [Table: see text]

THE PROGNOSTIC INDICATOR OF TUMOR INFILTRATING LYMPHOCYTES IN BREAST CARCINOMA

Introduction: Breast cancer is one of the common malignant tumors in women. The use of biomarkers ensures breast cancer patients receive optimal treatment. Tumor-infiltrating lymphocytes (TILs) are emerging as one of the key prognostic markers of breast cancer. Our study aims to evaluate percentage of TILs in Objectives And Methodology: tumor tissue, grading TILs based on the recommendations by an International TIL Working Group 2014 & compare with ER & PR status and in relation to concentration of TILs we assess prognosis of breast carcinoma for a period of 6 months. Results: Among 30 study subjects, TILs were of intermediate, high & lower grade in 53.3%, 40% and 6.7% cases respectively. TILs expression was statistically significant in both ER and PR, positive & negative groups (p<0.05). TILs were statistically highly significant as a prognostic marker in hormone negative breast cancers (p<0.05). Conclusion: Our study concludes that high TILs are correlated with favourable survival and response to treatment in breast cancer patients with ER, PR negative molecular subtype

The Tumor-Specific Expression of L1 Retrotransposons Independently Correlates with Time to Relapse in Hormone-Negative Breast Cancer Patients.

Background: Long-Interspersed Nuclear Element (L1) retrotransposons are silenced in healthy tissues but unrepressed in cancer. Even if L1 reactivation has been associated with reduced overall survival in breast cancer (BC) patients, a comprehensive correlation with clinicopathological features is still missing. Methods: Using quantitative, reverse-transcription PCR, we assessed L1 mRNA expression in 12 BC cells, 210 BC patients and in 47 normal mammary tissues. L1 expression was then correlated with molecular and clinicopathological data. Results: We identified a tumor-exclusive expression of L1s, absent in normal mammary cells and tissues. A positive correlation between L1 expression and tumor dedifferentiation, lymph-node involvement and increased immune infiltration was detected. Molecular subtyping highlighted an enrichment of L1s in basal-like cells and cancers. By exploring disease-free survival, we identified L1 overexpression as an independent biomarker for patients with a high risk of recurrence in hormone-receptor-negative BCs. Conclusions: Overall, L1 reactivation identified BCs with aggressive features and patients with a worse clinical fate.

Impact of HIV infection on overall survival among women with stage IV breast cancer in South Africa.

Advanced breast cancer (BC) at diagnosis is common in sub-Saharan Africa (SSA), including among women living with HIV (WLWH). In public hospitals across South Africa (SA), 10-15% of women present with stage IV BC, compared to < 5% in the United States (US); 20% of new BC diagnoses in SA are in WLWH. We evaluated the impact of HIV on overall survival (OS) among women with stage IV BC. We conducted a prospective cohort study of women diagnosed with stage IV BC between February 2, 2015 and September 18, 2019 at six public hospitals in SA. Multivariate Cox regression models were used to estimate the association between HIV status and OS. Among 550 eligible women, 147 (26.7%) were WLWH. Compared to HIV-negative BC patients, WLWH were younger (median age 45 vs. 60years, p < 0.001), predominantly black (95.9% vs. 77.9%, p < 0.001), and more likely to have hormone receptor-negative (hormone-negative) BC (32.7% vs. 22.6%, p = 0.016). Most women received systemic cancer-directed therapy (80.1%). HIV status was not associated with treatment or OS (Hazard Ratio (HR) 1.13 [95%CI 0.89-1.44]). On exploratory subgroup analysis, WLWH and hormone-negative BC had shorter OS compared to HIV-uninfected women (1-year OS: 27.1% vs. 48.8%, p = 0.003; HR 1.94 [95%CI 1.27-2.94]; p = 0.002), which was not observed for hormone receptor-positive BC. HIV status was not associated with worse OS in women with stage IV BC in SA and cannot account for the poor survival in this cohort. Subgroup analysis revealed that WLWH with hormone-negative BC had worse OS, which warrants further investigation.

Greater Survival Improvement in African American vs. Caucasian Women with Hormone Negative Breast Cancer.

Background: African American women have not benefited equally from recently improved breast cancer survival. We investigated if this was true for all subsets.Methods: We identified 395,170 patients with breast adenocarcinoma from the SEER database from 1990 to 2011 with designated race, age, stage, grade, ER and PR status, marital status and laterality, as control. We grouped patients into two time periods, 1990-2000 and 2001-2011, three age categories, under 40, 40-69 and ≥ 70 years and two stage categories, I-III and IV. We used the Kaplan-Meier and logrank tests to compare survival curves. We stratified data by patient- and tumor-associated variables to determine co-variation among confounding factors using the Pearson Chi-square test and Cox proportional hazards regression to determine hazard ratios (HR) to compare survival.Results: Stage I-III patients of both races ≥ 70 years old, African American widowed patients and Caucasians with ER- and PR- tumors had worse improvements in survival in 2001-2011 than younger, married or hormone receptor positive patients, respectively. In contrast, African Americans with ER- (Cox HR 0.70 [95% CI 0.65-0.76]) and PR- (Cox HR 0.67 [95% CI 0.62-0.72]) had greater improvement in survival in 2001-2011 than Caucasians with ER- (Cox HR 0.81 [95% CI 0.78-0.84]) and PR- disease (Cox HR 0.75 [95% CI 0.73-0.78]). This was not associated with changes in distribution of tumor or patient attributes.Conclusions: African American women with stage I-III ER- and PR- breast cancer had greater improvement in survival than Caucasians in 2001-2011. This is the first report of an improvement in racial disparities in survival from breast cancer in a subset of patients.

Vitamin D Receptor in Breast Cancer Tissues and Its Relation to Estrogen Receptor Alpha (ER-α) Gene Expression and Serum 25-hydroxyvitamin D Levels in Egyptian Breast Cancer Patients: A Case-control Study

IntroductionThis study aimed to explore the role of vitamin D receptor (VDR) in breast cancer tissues and its relation to serum 25-hydroxyvitamin D [25(OH)D] levels and estrogen receptor alpha (ER-α) gene expression in patients with breast cancer. Patients and MethodsCancerous and normal breast tissues from 40 women with breast cancer were analyzed for quantification of VDR levels and ER-α gene expression. The serum levels of 25(OH)D were measured in patients with breast cancer and controls by radioimmunoassay. ResultsPatients with breast cancer had serum levels of 25(OH)D significantly lower than normal control subjects. The levels of VDR and ER-α were significantly higher in breast cancer tissues than in normal breast tissues. The serum levels of 25(OH)D were indirectly and significantly correlated with the tissue levels of both VDR and ER-α gene expression. There was a significant direct correlation between the tissue levels of VDR and ER-α gene expression. The serum 25(OH) D levels, tissue VDR levels, and ER-α gene expression levels were inversely and significantly correlated with breast cancer histopathologic grade. Women with serum 25(OH)D levels ≤ 30 nmol/L, tissue levels of VDR > 5 ng/mL, and tissue levels of ER-α gene expression > 17.7 copies had significantly increased risk for breast cancer incidence. ConclusionWomen with low serum 25(OH)D levels, high tissue levels of VDR, and ER-α gene expression had increased risk for breast cancer. VDR are upregulated in breast cancer tissues thus it may be used for target therapy especially in hormone-negative breast cancer.

Abstract B58: Modeling oncogenic events in breast cancer precursor cells to study cancer evolution and genomic instability

Abstract Introduction: Over recent years, our knowledge of breast cancer biology has greatly improved; however, the mechanisms of tumor initiation and genomic drivers of this disease remain poorly understood. Hormone-negative breast cancers, such as triple-negative breast cancer (TNBC), are specifically challenging to treat, since they are genetically heterogeneous, often aggressive, and lack targetable driver mutation. Most TNBCs (80%) are basal-like (BLBC) and the majority of BLBCs harbor pathogenic mutations in TP53 tumor-suppressor gene (84%), indicating that TP53 plays a critical role in the pathogenesis of this cancer. Other less frequently observed alterations include mutation or epigenetic silencing of BRCA1/2 genes (36%), amplifications of oncogenes (MYC 40%, CCNE1 9%), and mutations or deletions of tumor suppressors (PTEN 35%, RB1 20%). Unfortunately, none of these genetic aberrations is currently druggable, mostly due to the lack of specific inhibitors. However, modeling these oncogenic events in precursor cells will enable us to study cancer evolution and acquisition of genomic instability. Experimental Procedures: We used basal-like mammary epithelial cells, MCF10A and MCF12A, to generate precursor models of TNBC. We overexpressed in these cell lines a hotspot p53 mutation (R175H), which demonstrates a dominant-negative phenotype. We confirmed that ectopic expression of R175H p53MUT impairs the ability of p53WT to properly respond to DNA damage induced by hydroxyurea or etoposide. As a result, cells fail to elevate the expression of p53 downstream targets, such as CDKN1A (cell cycle inhibitor), PUMA, BAX, and MDM2 (apoptosis regulators). Using CRISPR/Cas9-mediated genome editing we further performed depletion of RB1, PTEN, BRCA1, and BRCA2 genes in derived precursor models. Depletion of olfactory receptors OR10A4 and OR2W5 was performed as a control. In addition, we overexpressed S. pyogenes Cas9 endonuclease in these cell lines, in order to utilize them in CRISPR/Cas9-based gene knockout screens. Multiplexed functional analysis of CRISPR/Cas9-induced genomic alterations can be performed with lentiviral gRNA-based libraries in Cas9-expressing cells. All modified cell lines were clonally derived and gene depletion was validated with qRT-PCR and Western blot. Cas9 efficacy was confirmed with doxycycline-inducible RB1 knockout verified by T7 Endonuclease I genotyping assay. We further performed a range of phenotypic assays, such as proliferation, migration, anchorage-independent growth, and genomic instability assays, to measure the gain of tumorigenic properties upon acquisition of different genomic alterations. Summary: We established breast cancer precursor cell line models harboring genomic alterations in tumor suppressor genes commonly altered in TNBC, such as p53, RB1, PTEN, BRCA1, and BRCA2. Conclusions: Studying early transformation events leading to development of TNBC is necessary for understanding the etiology of this disease and identifying therapeutic vulnerabilities of precancerous lesions. To our knowledge, no comprehensive repertoire of breast cancer precursor models has been derived before. Also, ectopic expression of Cas9 in these cell lines makes them suitable for CRISPR/Cas9-based genomic screens to study disease evolution. CRISPR/Cas9 screens represent powerful tools to understand pathogenicity of different mutation events in disease initiation and progression. The use of genomically stable precursor cells in such studies makes the initial identification of putative drivers easier to define, in contrast to cancer cell lines, in which various compensatory pathways have evolved to cope with high genomic instability. Thus, established precursor models can be utilized in large-scale CRISPR/Cas9 screens focused on discovery of therapeutic targets, synthetic lethality, and genomic drivers of TNBC. Citation Format: Justyna Kanska, Kruttika Dabke, Simon A. Gayther. Modeling oncogenic events in breast cancer precursor cells to study cancer evolution and genomic instability [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr B58.

Androgen receptor expression in hormone-negative breast cancers and its prognostic significance

Background/aim Breast carcinoma is a common, yet heterogeneous aggressive disease affecting relatively young patients. The androgen receptor (AR) is expressed in majority of breast cancers and across the main breast cancer subtypes. The aim of this study was to evaluate AR expression in hormone-negative breast cancer subtypes. Materials and methods Sixty cases of breast cancer were involved in this study; the samples were received in the Department of Pathology of Kasr El-Aini Hospital, Cairo University, Egypt. The expression of AR and human epidermal growth factor receptor-2 receptors were studied by immunohistochemistry in 60 formalin-fixed paraffin-embedded selected hormone-negative breast cancer surgical specimens. The immunohistochemistry expression of the marker was correlated with the clinicopathological variables. Results Of the hormone-negative cases, 61.6% show positive AR expression, 89% of which are invasive duct carcinoma, 68.3% are associated with ductal carcinoma in situ, and 55% are human epidermal growth factor receptor-2-enriched subtype. A significant correlation was found between the AR expression and tumor type. There is no evident significant correlation with tumor grade, multicentricity or lymphovascular invasion. Conclusion The AR has recently emerged as a useful marker for the further refinement of breast cancer subtype classification. Antiandrogens are thought to markedly enhance treatments and to be the first targeted therapy in hormone-negative breast cancer cases.

BARHL1 Is Downregulated in Alzheimer's Disease and May Regulate Cognitive Functions through ESR1 and Multiple Pathways.

The Transcription factor BarH like homeobox 1 (BARHL1) is overexpressed in medulloblastoma and plays a role in neurogenesis. However, much about the BARHL1 regulatory networks and their functions in neurodegenerative and neoplastic disorders is not yet known. In this study, using a tissue microarray (TMA), we report for the first time that BARHL1 is downregulated in hormone-negative breast cancers and Alzheimer’s disease (AD). Furthermore, using an integrative bioinformatics approach and mining knockout mouse data, we show that: (i) BARHL1 and Estrogen Receptor 1 (ESR1) may constitute a network that regulates Neurotrophin 3 (NTF3)- and Brain Derived Neurotrophic Factor (BDNF)-mediated neurogenesis and neural survival; (ii) this is probably linked to AD pathways affecting aberrant post-translational modifications including SUMOylation and ubiquitination; (iii) the BARHL1-ESR1 network possibly regulates β-amyloid metabolism and memory; and (iv) hsa-mir-18a, having common key targets in the BARHL1-ESR1 network and AD pathway, may modulate neuron death, reduce β-amyloid processing and might also be involved in hearing and cognitive decline associated with AD. We have also hypothesized why estrogen replacement therapy improves AD condition. In addition, we have provided a feasible new mechanism to explain the abnormal function of mossy fibers and cerebellar granule cells related to memory and cognitive decline in AD apart from the Tau and amyloid pathogenesis through our BARHL1-ESR1 axis.

Low ATM protein expression in malignant tumor as well as cancer-associated stroma are independent prognostic factors in a retrospective study of early-stage hormone-negative breast cancer.

IntroductionThe serine/threonine protein kinase ataxia telangiectasia mutated (ATM) is critical in maintaining genomic integrity. Upon DNA double-strand breaks, ATM phosphorylates key downstream proteins including p53 and BRCA1/2, thereby orchestrating complex signaling pathways involved in cell cycle arrest, DNA repair, senescence and apoptosis. Although sporadic mutation of ATM occurs rarely in breast cancer, the status of its protein expression and its clinical significance in breast cancer remain not well established. Our study was designed to investigate the influence of ATM protein in both tumor and cancer-associated stroma on clinical outcome in hormone-positive (HPBC) and hormone-negative (HNBC) early-stage breast cancer (EBC).MethodsTissue microarrays (TMAs), containing formalin-fixed, paraffin-embedded resected tumors from two cohorts of patients (HPBC cohort: n = 130; HNBC cohort: n = 168) diagnosed at the Tom Baker Cancer Centre, Calgary, Canada, were analyzed for ATM protein expression using fluorescence immunohistochemistry (IHC) and automated quantitative analysis (AQUA). ATM expression levels were measured within the tumor as a whole (tATM) as indicated by pan-cytokeratin expression, tumor nuclear compartment (nATM) as indicated by both DAPI and pan-cytokeratin-positive results, and cancer-associated stroma (csATM) as indicated by vimentin-positive and pan-cytokeratin-negative results. ATM expression levels within these compartments were correlated with clinical outcome.ResultsWhile tATM and nATM were significantly lower in tumors compared to normal breast epithelial tissues, csATM was significantly higher than the corresponding normal tissue compartment. In addition, the median expression level of both tATM and nATM were two- to threefold lower (P <0.001) in HNBC than in HPBC. In both HNBC and HPBC cohorts, patients with low tATM, nATM and csATM tumors had significantly poorer survival outcomes than those with a high tATM, nATM and csATM, but this effect was more pronounced in HNBC. A multivariate analysis demonstrates that these biomarkers predict survival independent of tumor size and lymph node status, but only in the HNBC cohort (P <0.001).ConclusionsLow ATM protein expression in both malignant tumor and stromal compartments likely contributes to the aggressive nature of breast cancer and is an independent prognostic factor associated with worse survival in HNBC patients.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-015-0575-2) contains supplementary material, which is available to authorized users.

Intersection of FOXO- and RUNX1-mediated gene expression programs in single breast epithelial cells during morphogenesis and tumor progression

Gene expression networks are complicated by the assortment of regulatory factors that bind DNA and modulate transcription combinatorially. Single-cell measurements can reveal biological mechanisms hidden by population averages, but their value has not been fully explored in the context of mRNA regulation. Here, we adapted a single-cell expression profiling technique to examine the gene expression program downstream of Forkhead box O (FOXO) transcription factors during 3D breast epithelial acinar morphogenesis. By analyzing patterns of mRNA fluctuations among individual matrix-attached epithelial cells, we found that a subset of FOXO target genes was jointly regulated by the transcription factor Runt-related transcription factor 1 (RUNX1). Knockdown of RUNX1 causes hyperproliferation and abnormal morphogenesis, both of which require normal FOXO function. Down-regulating RUNX1 and FOXOs simultaneously causes widespread oxidative stress, which arrests proliferation and restores normal acinar morphology. In hormone-negative breast cancers lacking human epidermal growth factor receptor 2 (HER2) amplification, we find that RUNX1 down-regulation is strongly associated with up-regulation of FOXO1, which may be required to support growth of RUNX1-negative tumors. The coordinate function of these two tumor suppressors may provide a failsafe mechanism that inhibits cancer progression.

Red Meat Intake and Risk of Breast Cancer Among Premenopausal Women

Case-control and ecological studies have suggested that eating red meat increases the risk of breast cancer, but any putative association remains far from clear. Previous studies have generally focused on diet in mid-life or later. Conceivably components of red meat such as heterocyclic amines, heme iron, and residual exogenous hormones, which have estrogenic properties, could influence the breast cancer risk through actions on hormone receptors. A previous analysis of premenopausal women 26 to 46 years of age in the Nurses’ Health Study II (NHS-II) disclosed that animal fat intake did correlate with the risk of breast cancer. In addition, there was indication of an association with eating red meat—a major food source of animal fat. Four added years of follow-up now are available for analysis. The NHS-II cohort consists of 116,671 female registered nurses who have been followed up since 1989. A semiquantitative food frequency questionnaire was sent to participants in 1991, 1995, and 1999. During 12 years of follow-up of 90,659 women through 2003, 1021 invasive breast cancers were documented in premenopausal women. Of 789 cancers with available data, 512 were positive for both estrogen receptor (ER) and progesterone receptor (PR). For all cancers, the highest intake of red meat was only weakly—and not significantly—associated with breast cancer, but a strong association was evident for ER+/PR+ tumors. No such association was found for ER−/PR− breast cancers. Compared with eating 3 or fewer servings of red meat each week, the multivariate risk ratio for ER+/PR+ breast cancer was 1.l4 (95% Confidence Interval, 0.90–1.45) for more than 3 to 5 or fewer servings per week; 1.42 (1.06–1.90) for more than 5 servings per week to 1 or fewer servings per day; 1.20 (0.89–1.63) for more than 1 to 1.5 or fewer servings per day; and 1.97 (1.35–2.88) for more than 1.5 servings per day. The respective relative risk figures for ER−/PR− breast cancer were 1.34, 1.21, 0.69, and 0.89. High intake of several individual red meat items also correlated with an increased risk of hormone-positive breast cancer. The difference in results between hormone-positive and hormone-negative breast cancers was statistically significant. Comparable results were obtained when grams were estimated rather than serving sizes of red meat intake, and also when quintiles of intake were calculated. Neither adjusting for other food groups nor excluding cancers diagnosed during the first 2 years of follow-up altered the findings. The relationship was stronger for cumulative average intake rather than for baseline or most recent intake. Eating red meat was associated with an increased risk of hormone receptor-positive breast cancer in this large population of relatively young premenopausal women. The findings deserve further evaluation because of their public health implications. Unlike most risk factors for breast cancer, this one can readily be modified.