RESUMO
BACKGROUND: Breast cancer outcomes among patients who use safety-net hospitals in the highly populated Harris County, Texas and Southeast Brazil are poor. It is unknown whether treatment delay contributes to these outcomes. METHODS: We conducted a retrospective cohort analysis of patients with non-metastatic breast cancer diagnosed between January 1, 2009 and December 31, 2011 at Harris Health Texas and Unicamp's Women's Hospital, Barretos Hospital, and Brazilian National Institute of Cancer, Brazil. We used Cox proportional hazards regression to evaluate association of time to treatment and risk of recurrence (ROR) or death. RESULTS: One thousand one hundred ninety-one patients were included. Women in Brazil were more frequently diagnosed with stage III disease (32.3% vs. 21.1% Texas; P = .002). Majority of patients in both populations had symptom-detected disease (63% in Brazil vs. 59% in Texas). Recurrence within 5 years from diagnosis was similar 21% versus 23%. Median time from diagnosis to first treatment defined as either systemic therapy (chemotherapy or endocrine therapy) or surgery, were comparable, 9.9 weeks versus 9.4 weeks. Treatment delay was not associated with increased ROR or death. Higher stage at diagnosis was associated with both increased ROR and death. CONCLUSION: Time from symptoms to treatment was considerably long in both populations. Treatment delay did not affect outcomes. IMPACT: Access to timely screening and diagnosis of breast cancer are priorities in these populations.
Assuntos
Neoplasias da Mama , Brasil/epidemiologia , Neoplasias da Mama/diagnóstico , Neoplasias da Mama/epidemiologia , Neoplasias da Mama/terapia , Feminino , Humanos , Programas de Rastreamento , Estudos Retrospectivos , Tempo para o TratamentoRESUMO
PURPOSE: Neoadjuvant endocrine therapy (NET) has been shown to be effective in ER-positive/HER2-negative breast cancer in clinical trials. However, adoption in clinical practice is still limited. Real-world data may provide useful insights into effectiveness, toxicities and quality of care, potentially rendering clinical trial results to the real-world setting. Our purpose was to report real-world data of a cohort of postmenopausal patients submitted to NET. METHODS: This prospective cohort study evaluated 146 postmenopausal female patients with ER-positive/HER2-negative breast cancer treated with NET at three tertiary hospitals between 2016 and 2018. Clinicopathological information were collected prospectively. Preoperative Endocrine Prognostic Index (PEPI) score was calculated for tumors submitted to at least 16 weeks of NET. RESULTS: Median age was 67 years old, and 87.8% had stage I-II disease. Most tumors had histological grade II (76.1%). Median pretreatment Ki67 expression was 10%. Aromatase inhibitor was used in 99.5% of patients, and median treatment duration was 21.0 weeks. No tumor progressed during NET. Breast-conserving surgery was performed in the majority of patients (63.0%), as well as sentinel lymph-node biopsy (76.7%). Pathological complete response rate was 1.0%. 43 patients (29.5%) had PEPI score 0, and 26% had PEPI scores 4-5. Posttreatment Ki67 median expression was 3.0%, and only five tumors (3.4%) showed marked increase in Ki67 expression during treatment. Seven patients (4.8%) had HER2-positive residual disease, and were treated with adjuvant chemotherapy plus trastuzumab. CONCLUSIONS: Our real-world data shows that NET is effective and safe in postmenopausal patients with ER-positive/HER2-negative breast cancer. Postmenopausal status and low-risk luminal tumor features (luminal A-like) should be used as selection criteria to ensure the best results with NET.
Assuntos
Neoplasias da Mama , Terapia Neoadjuvante , Idoso , Inibidores da Aromatase/uso terapêutico , Neoplasias da Mama/tratamento farmacológico , Feminino , Humanos , Estudos Prospectivos , Receptor ErbB-2/genética , Receptores de EstrogênioRESUMO
Introduction: Mutations in the ESR1 gene (ESR1m) are important mechanisms of resistance to endocrine therapy in estrogen receptor-positive (ER+) metastatic breast cancer and have been studied as a potential therapeutic target, as well as a predictive and prognostic biomarker. Nonetheless, the role of ESR1m as a possible mechanism of primary endocrine resistance, as well as whether it also occurs in tumors that are resistant to ET administered in early-stage disease as (neo)adjuvant, has not been adequately studied. In this study, we evaluated the prevalence of ESR1m in tumor samples from patients with ER+ breast cancer resistant to neoadjuvant aromatase inhibitor therapy. Methods: We followed a prospective cohort of patients with ER+ HER2- stages II and III breast cancer treated with neoadjuvant endocrine therapy (NET). Tumor samples from patients with a pattern of primary endocrine resistance [defined as a Preoperative Endocrine Prognostic Index (PEPI) score of ≥4] were identified and analyzed for the presence of ESR1m. Results: One hundred twenty-seven patients were included in the cohort, of which 100 (79%) had completed NET and underwent surgery. Among these patients, the PEPI score ranged from 0 to 3 in 70% (70/100), whereas 30% (30/100) had a PEPI score of 4 or more. Twenty-three of these patients were included in the analysis. ESR1 mutations were not identified in any of the 23 patients with early-stage ER+ breast cancer resistant to NET. Discussion: Growing evidence supports the notion that there are different mechanisms for primary and secondary endocrine resistance. Our study suggests that ESR1 mutations do not evolve rapidly and do not represent a common mechanism of primary endocrine resistance in the neoadjuvant setting. Therefore, ESR1m should be considered a mechanism of acquired endocrine resistance in the context of advanced disease. Further research should be conducted to identify factors associated with intrinsic resistance to ET.
RESUMO
BACKGROUND: As the most incident tumor among women worldwide, breast cancer is a heterogeneous disease. Tremendous efforts have been made to understand how tumor characteristics as histological type, molecular subtype, and tumor microenvironment collectively influence disease diagnosis to treatment, which impact outcomes. Differences between populations and environmental and cultural factors have impacts on the origin and evolution of the disease, as well as the therapeutic challenges that arise due to these factors. We, then, compared copy number variations (CNVs) in mucinous and nonmucinous luminal breast tumors from a Brazilian cohort to investigate major CNV imbalances in mucinous tumors versus non-mucinous luminal tumors, taking into account their clinical and pathological features. METHODS: 48 breast tumor samples and 48 matched control blood samples from Brazilian women were assessed for CNVs by chromosome microarray. Logistic regression and random forest models were used in order to assess CNVs in chromosomal regions from tumors. RESULTS: CNVs that were identified in chromosomes 1, 5, 8, 17, 19, and 21 classify tumors according to their histological type, ethnicity, disease stage, and familial history. CONCLUSION: Copy number alterations described in this study provide a better understanding of the landscape of genomic aberrations in mucinous breast cancers that are associated with clinical features.
Assuntos
Neoplasias da Mama/genética , Variações do Número de Cópias de DNA/genética , Adenocarcinoma Mucinoso/genética , Adulto , Brasil/epidemiologia , Carcinoma Ductal de Mama/genética , Estudos de Coortes , Feminino , Genômica/métodos , Humanos , Pessoa de Meia-Idade , Análise de Sequência com Séries de Oligonucleotídeos/métodos , Microambiente Tumoral/genéticaRESUMO
Importance: Pathologic complete response rate (pCR), the primary end point of the ACOSOG (American College of Surgeons Oncology Group) Z1041 (Alliance) trial, and disease-free survival (DFS) and overall survival (OS) in women with operable HER2-positive breast cancer are similar between treatment regimens. Objective: To assess DFS and OS for patients treated with sequential vs concurrent anthracycline plus trastuzumab. Design, Setting, and Participants: Phase 3 randomized clinical trial conducted at 36 centers in the continental United States and Puerto Rico. Women 18 years or older with invasive operable HER2-positive breast cancer were enrolled from September 15, 2007, to December 15, 2011, and randomized to 1 of 2 treatment arms. The analysis data set was locked on October 15, 2017, and analysis was completed on December 15, 2017. Interventions: Patients randomized to arm 1 received 500 mg/m2 of fluorouracil, 75 mg/m2 of epirubicin, and 500 mg/m2 of cyclophosphamide (FEC) every 3 weeks for 12 weeks followed by the combination of 80 mg/m2 of paclitaxel and 2 mg/kg (except initial dose of 4 mg/kg) of trastuzumab weekly for 12 weeks. Patients randomized to arm 2 received the same combination of paclitaxel with trastuzumab weekly for 12 weeks followed by FEC every 3 weeks with weekly trastuzumab for 12 weeks. Women with hormone receptor-positive disease received endocrine therapy, and radiotherapy was delivered at physician discretion. Main Outcomes and Measures: The primary outcomes were DFS and OS and pCR in the breast and nodes. Results: Two hundred eighty-two women with HER2-positive breast cancer were enrolled in the trial, and 2 withdrew consent before treatment. Among the remaining 280 women, the median age was 50 years (range, 28-76 years), 232 (82.9%) were white, 29 (10.3%) were black, 8 (2.9%) were Asian, 4 (1.4%) were American Indian or Alaskan Native, and 7 (2.5%) did not report race/ethnicity. There were 22 disease events in arm 1 and 27 in arm 2. Disease-free survival rates did not differ with respect to treatment arm (stratified log-rank P = .96; stratified hazard ratio [HR] [arm 2 to arm 1], 1.02; 95% CI, 0.56-1.83). Overall survival did not differ with respect to treatment arm (stratified log-rank P = .73; stratified HR [arm 2 to arm 1], 1.17; 95% CI, 0.48-2.88). Conclusions and Relevance: Across a median follow-up of 5.1 years (range, 26 days to 6.2 years), pCR, DFS, and OS did not differ with respect to sequential or concurrent administration of FEC with trastuzumab. Trial Registration: ClinicalTrials.gov identifier: NCT00513292.
Assuntos
Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Biomarcadores Tumorais/análise , Neoplasias da Mama/tratamento farmacológico , Terapia Neoadjuvante , Receptor ErbB-2/análise , Adulto , Idoso , Protocolos de Quimioterapia Combinada Antineoplásica/efeitos adversos , Neoplasias da Mama/química , Neoplasias da Mama/mortalidade , Neoplasias da Mama/patologia , Quimioterapia Adjuvante , Ciclofosfamida/administração & dosagem , Progressão da Doença , Esquema de Medicação , Epirubicina/administração & dosagem , Feminino , Fluoruracila/administração & dosagem , Humanos , Pessoa de Meia-Idade , Terapia Neoadjuvante/efeitos adversos , Terapia Neoadjuvante/mortalidade , Paclitaxel/administração & dosagem , Intervalo Livre de Progressão , Porto Rico , Fatores de Risco , Fatores de Tempo , Trastuzumab/administração & dosagem , Estados UnidosRESUMO
The estrogen receptor (ER) has been targeted for breast cancer treatment for over a century, but many challenges persist. ER-positivity identifies the largest breast cancer subgroup, and ER-directed therapies prolong survival and improve symptoms in the advanced setting with a very favorable side effect profile. Treatment strategies have included decreasing estrogen synthesis and modulating or degrading the ER. However, ER+ breast cancer once diagnosed in the advanced setting still represents an incurable condition. Many efforts are ongoing to circumvent resistance mechanisms with a few strategies already incorporated into clinical practice such as the combination of endocrine agents with drugs that interfere with other signaling pathways and cell-cycle progression. Important questions remain as how best to select each available strategy, how to sequence them and ultimately how to extend benefits to the largest number of patients in need.
Assuntos
Antineoplásicos Hormonais/uso terapêutico , Neoplasias da Mama/tratamento farmacológico , Receptor ErbB-2/metabolismo , Receptores de Estrogênio/metabolismo , Neoplasias da Mama/genética , Neoplasias da Mama/metabolismo , Neoplasias da Mama/patologia , Feminino , Humanos , Metástase Neoplásica , Receptor ErbB-2/genética , Receptores de Estrogênio/genéticaRESUMO
BACKGROUND: Cancer is the second leading cause of death in the Caribbean, including the islands of Trinidad and Tobago (TT). The population of TT consists of over 1.3 million people with diverse ancestral and sociocultural backgrounds, both of which may influence cancer incidence and mortality. The objective of this study was to examine incidence and mortality patterns and trends in TT. METHODS: Cancer surveillance data on 29,512 incident cancer cases reported to the Dr. Elizabeth Quamina Cancer Registry (population-based cancer registry of TT) between 1995 and 2009 were analyzed. Age-standardized rates, overall and by sex, ancestry, and geography, were reported. RESULTS: The highest incidence and mortality rates were observed for cancers related to reproductive organs in women, namely, breast, cervical, and uterine cancers, and prostate, lung and colorectal cancers among men. Average incidence rates were highest in areas covered by the Tobago Regional Health Authority (TRHA) (188 per 100,000), while average mortality rates were highest in areas covered by the North West Regional Health Authority (108 per 100,000). Nationals of African ancestry exhibited the highest rates of cancer incidence (243 per 100,000) and mortality (156 per 100,000) compared to their counterparts who were of East Indian (incidence, 125 per 100,000; mortality, 66 per 100,000) or mixed ancestry (incidence, 119 per 100,000; mortality, 66 per 100,000). CONCLUSIONS: Our findings highlight the need for national investment to improve the understanding of the epidemiology of cancer in Trinidad and Tobago, and to ultimately guide much needed cancer prevention and control initiatives in the near future.
Assuntos
Neoplasias/epidemiologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Detecção Precoce de Câncer , Feminino , Humanos , Incidência , Masculino , Pessoa de Meia-Idade , Estadiamento de Neoplasias , Neoplasias/mortalidade , Neoplasias/prevenção & controle , Trinidad e Tobago/epidemiologiaRESUMO
OPINION STATEMENT: Neoadjuvant endocrine therapy (NET) with Ki67-based response monitoring is a practical, cost-effective approach to the management of clinical stage II and III estrogen receptor-positive (ER+) breast cancer. In addition to marked improvements in rates of breast conservation, the identification of extreme responders on the basis of the preoperative endocrine prognostic index (PEPI) provides a rationale to avoid chemotherapy on the basis of highly favorable prognosis in some patients. Finally, samples accrued from patients treated with neoadjuvant therapy are providing valuable insights into the molecular basis for intrinsic resistance to endocrine therapy and promise a more rational basis and precise approach to the systemic treatment of ER+ breast cancer.
Assuntos
Antineoplásicos Hormonais/uso terapêutico , Neoplasias da Mama/tratamento farmacológico , Terapia de Reposição Hormonal , Terapia Neoadjuvante , Neoplasias da Mama/genética , Neoplasias da Mama/patologia , Feminino , Humanos , Estadiamento de Neoplasias , Prognóstico , Receptores de Estrogênio/genética , Receptores de Progesterona/genéticaRESUMO
PURPOSE: The recent publication of the ACOSOG Z1031 trial results demonstrated that Ki-67 proliferation marker-based neoadjuvant endocrine therapy response monitoring could be used for tailoring the use of adjuvant chemotherapy in ER+HER2-negative breast cancer patients. In this paper, we describe the development of the Ki-67 clinical trial assay used for this study. METHODS: Ki-67 assay assessment focused on reproducing a 2.7% Ki-67 cut-point (CP) required for calculating the Preoperative Endocrine Prognostic Index and a 10% CP for poor endocrine therapy response identification within the first month of neoadjuvant endocrine treatment. Image analysis was assessed to increase the efficiency of the scoring process. Clinical outcome concordance for two independent Ki-67 scores was the primary performance metric. RESULTS: Discordant scores led to a triage approach where cases with complex histological features that software algorithms could not resolve were flagged for visual point counting (17%). The final Ki-67 scoring approach was run on T1/2 N0 cases from the P024 and POL trials (N = 58). The percent positive agreement for the 2.7% CP was 87.5% (95% CI 61.7-98.5%); percent negative agreement 88.9% (95% CI: 65.3-98.6%). Minor discordance did not affect the ability to predict similar relapse-free outcomes (Log-Rank P = 0.044 and P = 0.055). The data for the 10% early triage CP in the POL trial were similar (N = 66), the percentage positive agreement was 100%, and percent negative agreement 93.55% (95% CI: 78.58-99.21%). The independent survival predictions were concordant (Log-rank P = 0.0001 and P = 0.01). CONCLUSIONS: We have developed an efficient and reproducible Ki-67 scoring system that was approved by the Clinical Trials Evaluation Program for NCI-supported neoadjuvant endocrine therapy trials. Using the methodology described here, investigators are able to identify a subgroup of patients with ER+HER2-negative breast cancer that can be safely managed without the need of adjuvant chemotherapy.
Assuntos
Neoplasias da Mama/tratamento farmacológico , Neoplasias da Mama/metabolismo , Antígeno Ki-67/metabolismo , Antineoplásicos Hormonais/administração & dosagem , Antineoplásicos Hormonais/uso terapêutico , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Biomarcadores , Neoplasias da Mama/diagnóstico , Neoplasias da Mama/mortalidade , Quimioterapia Adjuvante , Tomada de Decisão Clínica , Feminino , Humanos , Estimativa de Kaplan-Meier , Terapia Neoadjuvante , Prognóstico , Curva ROC , Reprodutibilidade dos Testes , Resultado do TratamentoRESUMO
UNLABELLED: Breast cancer (BC) is the most common newly diagnosed cancer among women in Trinidad and Tobago (TT) and BC mortality rates are among the highest in the world. Globally, racial/ethnic trends in BC incidence, mortality and survival have been reported. However, such investigations have not been conducted in TT, which has been noted for its rich diversity. In this study, we investigated associations among ancestry, geography and BC incidence, mortality and survival in TT. Data on 3767 incident BC cases, reported to the National Cancer Registry of TT, from 1995 to 2007, were analyzed in this study. Women of African ancestry had significantly higher BC incidence and mortality rates ( INCIDENCE: 66.96; MORTALITY: 30.82 per 100,000) compared to women of East Indian ( INCIDENCE: 41.04, MORTALITY: 14.19 per 100,000) or mixed ancestry ( INCIDENCE: 36.72, MORTALITY: 13.80 per 100,000). Geographically, women residing in the North West Regional Health Authority (RHA) catchment area followed by the North Central RHA exhibited the highest incidence and mortality rates. Notable ancestral differences in survival were also observed. Women of East Indian and mixed ancestry experienced significantly longer survival than those of African ancestry. Differences in survival by geography were not observed. In TT, ancestry and geographical residence seem to be strong predictors of BC incidence and mortality rates. Additionally, disparities in survival by ancestry were found. These data should be considered in the design and implementation of strategies to reduce BC incidence and mortality rates in TT.
Assuntos
Neoplasias da Mama/epidemiologia , Neoplasias da Mama/etiologia , Adulto , Idoso , Neoplasias da Mama/diagnóstico , Neoplasias da Mama/terapia , Feminino , Geografia , Humanos , Incidência , Estimativa de Kaplan-Meier , Pessoa de Meia-Idade , Mortalidade , Gradação de Tumores , Estadiamento de Neoplasias , Vigilância da População , Modelos de Riscos Proporcionais , Sistema de Registros , Fatores de Risco , Trinidad e Tobago/epidemiologia , Trinidad e Tobago/etnologiaRESUMO
BACKGROUND: Neoadjuvant chemotherapy with trastuzumab for patients with HER2-positive breast cancer can produce a pathological complete response in the breast in 30-65% of patients. We investigated the effect of the timing of trastuzumab administration with anthracycline and taxane neoadjuvant chemotherapy. METHODS: This randomised trial was done at 36 centres in the USA and Puerto Rico. Women with operable HER2-positive invasive breast cancer were randomly assigned (1:1) with a biased coin minimisation algorithm, stratified for age, tumour size, and hormone receptor status. Neither patients nor investigators (except for a cardiac safety review panel) were masked to treatment assignment. Patients randomly assigned to sequential treatment received fluorouracil 500 mg/m(2), epirubicin 75 mg/m(2), and cyclophosphamide 500 mg/m(2) (FEC-75) on day 1 of a 21-day cycle for four cycles followed by paclitaxel 80 mg/m(2) and trastuzumab 2 mg/kg (after a 4 mg/kg loading dose) once per week for 12 weeks, while those randomly assigned to the concurrent treatment group received paclitaxel and trastuzumab once per week for 12 weeks followed by four cycles of FEC-75 (on day 1 of each 21-day cycle) and once-weekly trastuzumab, in the same doses as the sequential group. Surgery, including evaluation of the axilla, was done within 6 weeks of completion of neoadjuvant treatment. The primary outcome was the percentage of patients who had a pathological complete response in the intention-to-treat population. The study is registered with ClinicalTrials.gov, number NCT00513292. FINDINGS: From Sept 15, 2007, to Dec 15, 2011, 282 women were enrolled (140 in the sequential group, 142 in the concurrent group). Two patients in the sequential group withdrew consent before starting treatment. 78 of 138 (56·5%, 95% CI 47·8-64·9) patients who received sequential treatment had a pathological complete response in the breast versus 77 of 142 (54·2%, 95% CI 45·7-62·6) who received concurrent treatment (difference 2·3%, 95% CI -9·3 to 13·9). No treatment-related deaths occurred. The most common severe toxic effects were neutropenia (35 [25·3%] of 138 patients in the sequential group vs 45 [31·7%] of 142 patients in the concurrent group) and fatigue (six [4·3%] vs 12 [8·5%]). Left ventricular ejection fraction dropped below the institutional lower limit of normal at week 12 in one (0·8%) of 130 patients who received sequential treatment and four (2·9%) of 137 patients who received concurrent treatment; by week 24, it had dropped below this limit in nine (7·1%) of 126 patients and in six (4·6%) of 130 patients, respectively. INTERPRETATION: Concurrent administration of trastuzumab with anthracyclines offers no additional benefit and is not warranted. FUNDING: US National Cancer Institute.
Assuntos
Protocolos de Quimioterapia Combinada Antineoplásica/administração & dosagem , Protocolos de Quimioterapia Combinada Antineoplásica/efeitos adversos , Biomarcadores Tumorais/análise , Neoplasias da Mama/tratamento farmacológico , Mastectomia , Terapia Neoadjuvante/métodos , Receptor ErbB-2/análise , Adulto , Idoso , Anticorpos Monoclonais Humanizados/administração & dosagem , Anticorpos Monoclonais Humanizados/efeitos adversos , Neoplasias da Mama/química , Neoplasias da Mama/patologia , Neoplasias da Mama/cirurgia , Quimioterapia Adjuvante , Ciclofosfamida/administração & dosagem , Ciclofosfamida/efeitos adversos , Intervalo Livre de Doença , Esquema de Medicação , Epirubicina/administração & dosagem , Epirubicina/efeitos adversos , Feminino , Fluoruracila/administração & dosagem , Fluoruracila/efeitos adversos , Humanos , Estimativa de Kaplan-Meier , Linfonodos/patologia , Linfonodos/cirurgia , Metástase Linfática , Mastectomia/métodos , Pessoa de Meia-Idade , Gradação de Tumores , Estadiamento de Neoplasias , Paclitaxel/administração & dosagem , Paclitaxel/efeitos adversos , Porto Rico , Volume Sistólico/efeitos dos fármacos , Fatores de Tempo , Trastuzumab , Resultado do Tratamento , Estados UnidosRESUMO
A hormonioterapia neoadjuvante tem sido cada vez mais utilizada na prática clínica para melhorar as opções cirúrgicas para mulheres pós-menopáusicas com tumores localmente avançados, com receptores hormonais fortemente positivos. Estudos recentes indicam que a resposta do tumor nesta população pode prever o resultado em longo prazo de pacientes em terapia endócrina adjuvante, defendendo a sua ampla aplicação no tratamento da doença nas pacientes com receptores hormonais positivos. Nas pacientes na pré-menopausa, mais estudos são necessários para estabelecer o real benefício desta abordagem. Do ponto de vista de investigação, a hormonioterapia neoadjuvante pode proporcionar uma oportunidade única para os estudos preditores de resposta, além de proporcionar o desenvolvimento de novos agentes terapêuticos.
Assuntos
Humanos , Feminino , Pessoa de Meia-Idade , Neoplasias da Mama/epidemiologia , Neoplasias da Mama/tratamento farmacológico , Pré-Menopausa/metabolismoRESUMO
INTRODUCTION: Inhibition of phosphatidylinositol-3-kinase (PI3K) induces apoptosis when combined with estrogen deprivation in estrogen receptor (ER)-positive breast cancer. The aims of the present study were to identify effective PI3K pathway inhibitor and endocrine therapy combinations, to evaluate the effect of PI3K pathway mutations and estrogen dependency on tumor response, and to determine the relevance of PIK3CA mutation in recurrent disease. METHODS: The PI3K catalytic subunit inhibitor BKM120, the mammalian target of rapamycin (mTOR) inhibitor RAD001 and the dual PI3K/mTOR inhibitor BGT226 were tested against ER-positive breast cancer cell lines before and after long-term estrogen deprivation (LTED). The impact of estradiol deprivation and the ER downregulator fulvestrant on PI3K pathway inhibitor-induced apoptosis was assessed. PIK3CA hotspot mutation analysis was performed in 51 recurrent or metastatic breast cancers and correlated with ER status and survival. RESULTS: Drug-induced apoptosis was most marked in short-term estrogen-deprived cells with PIK3CA mutation and phosphatase and tensin homolog loss. Apoptosis was most highly induced by BGT226, followed by BKM120, and then RAD001. Estradiol antagonized PI3K inhibitor-induced apoptosis following short-term estrogen deprivation, emphasizing a role for estrogen-deprivation therapy in promoting PI3K inhibitor activity in the first-line setting. ER-positive MCF7 LTED cells exhibited relative resistance to PI3K pathway inhibition that was reversed by fulvestrant. In contrast, T47D LTED cells exhibited ER loss and ER-independent PI3K agent sensitivity. PIK3CA mutation was prevalent in relapsed ER-positive disease (48%) and was associated with persistent ER positivity and a late relapse pattern. CONCLUSIONS: Estrogen deprivation increased the apoptotic effects of PI3K and dual PI3K/mTOR inhibitors in ER-positive disease, providing a rationale for PI3K/aromatase inhibitor combinations as first-line therapy. In LTED cells, differential effects on ER expression may be a relevant consideration. When ER was persistently expressed, fulvestrant strongly promoted PI3K drug activity. When ER was lost, PI3K inhibitor monotherapy was sufficient to induce high-level apoptosis. Although tumors with PIK3CA mutation had a late recurrence pattern, these mutations were common in metastatic disease and were most often associated with persistent ER expression. Targeting PIK3CA mutant tumors with a PI3K pathway inhibitor and fulvestrant is therefore a feasible strategy for aromatase-inhibitor-resistant ER-positive relapsed breast cancer.