RESUMO
BACKGROUND: The TARGIT-A trial compared risk-adapted radiotherapy using single-dose targeted intraoperative radiotherapy (TARGIT) versus fractionated external beam radiotherapy (EBRT) for breast cancer. We report 5-year results for local recurrence and the first analysis of overall survival. METHODS: TARGIT-A was a randomised, non-inferiority trial. Women aged 45 years and older with invasive ductal carcinoma were enrolled and randomly assigned in a 1:1 ratio to receive TARGIT or whole-breast EBRT, with blocks stratified by centre and by timing of delivery of targeted intraoperative radiotherapy: randomisation occurred either before lumpectomy (prepathology stratum, TARGIT concurrent with lumpectomy) or after lumpectomy (postpathology stratum, TARGIT given subsequently by reopening the wound). Patients in the TARGIT group received supplemental EBRT (excluding a boost) if unforeseen adverse features were detected on final pathology, thus radiotherapy was risk-adapted. The primary outcome was absolute difference in local recurrence in the conserved breast, with a prespecified non-inferiority margin of 2·5% at 5 years; prespecified analyses included outcomes as per timing of randomisation in relation to lumpectomy. Secondary outcomes included complications and mortality. This study is registered with ClinicalTrials.gov, number NCT00983684. FINDINGS: Patients were enrolled at 33 centres in 11 countries, between March 24, 2000, and June 25, 2012. 1721 patients were randomised to TARGIT and 1730 to EBRT. Supplemental EBRT after TARGIT was necessary in 15·2% [239 of 1571] of patients who received TARGIT (21·6% prepathology, 3·6% postpathology). 3451 patients had a median follow-up of 2 years and 5 months (IQR 12-52 months), 2020 of 4 years, and 1222 of 5 years. The 5-year risk for local recurrence in the conserved breast was 3·3% (95% CI 2·1-5·1) for TARGIT versus 1·3% (0·7-2·5) for EBRT (p=0·042). TARGIT concurrently with lumpectomy (prepathology, n=2298) had much the same results as EBRT: 2·1% (1·1-4·2) versus 1·1% (0·5-2·5; p=0·31). With delayed TARGIT (postpathology, n=1153) the between-group difference was larger than 2·5% (TARGIT 5·4% [3·0-9·7] vs EBRT 1·7% [0·6-4·9]; p=0·069). Overall, breast cancer mortality was much the same between groups (2·6% [1·5-4·3] for TARGIT vs 1·9% [1·1-3·2] for EBRT; p=0·56) but there were significantly fewer non-breast-cancer deaths with TARGIT (1·4% [0·8-2·5] vs 3·5% [2·3-5·2]; p=0·0086), attributable to fewer deaths from cardiovascular causes and other cancers. Overall mortality was 3·9% (2·7-5·8) for TARGIT versus 5·3% (3·9-7·3) for EBRT (p=0·099). Wound-related complications were much the same between groups but grade 3 or 4 skin complications were significantly reduced with TARGIT (four of 1720 vs 13 of 1731, p=0·029). INTERPRETATION: TARGIT concurrent with lumpectomy within a risk-adapted approach should be considered as an option for eligible patients with breast cancer carefully selected as per the TARGIT-A trial protocol, as an alternative to postoperative EBRT. FUNDING: University College London Hospitals (UCLH)/UCL Comprehensive Biomedical Research Centre, UCLH Charities, National Institute for Health Research Health Technology Assessment programme, Ninewells Cancer Campaign, National Health and Medical Research Council, and German Federal Ministry of Education and Research.
Assuntos
Neoplasias da Mama/radioterapia , Carcinoma Ductal de Mama/radioterapia , Idoso , Neoplasias da Mama/mortalidade , Neoplasias da Mama/cirurgia , Carcinoma Ductal de Mama/mortalidade , Carcinoma Ductal de Mama/cirurgia , Feminino , Humanos , Cuidados Intraoperatórios/métodos , Cuidados Intraoperatórios/mortalidade , Estimativa de Kaplan-Meier , Mastectomia Segmentar/métodos , Mastectomia Segmentar/mortalidade , Pessoa de Meia-Idade , Recidiva Local de Neoplasia/mortalidade , Recidiva Local de Neoplasia/prevenção & controle , Radioterapia/métodos , Radioterapia/mortalidade , Resultado do TratamentoRESUMO
BACKGROUND: 5-year results of the UK Standardisation of Breast Radiotherapy (START) trials suggested that lower total doses of radiotherapy delivered in fewer, larger doses (fractions) are at least as safe and effective as the historical standard regimen (50 Gy in 25 fractions) for women after primary surgery for early breast cancer. In this prespecified analysis, we report the 10-year follow-up of the START trials testing 13 fraction and 15 fraction regimens. METHODS: From 1999 to 2002, women with completely excised invasive breast cancer (pT1-3a, pN0-1, M0) were enrolled from 35 UK radiotherapy centres. Patients were randomly assigned to a treatment regimen after primary surgery followed by chemotherapy and endocrine treatment (where prescribed). Randomisation was computer-generated and stratified by centre, type of primary surgery (breast-conservation surgery or mastectomy), and tumour bed boost radiotherapy. In START-A, a regimen of 50 Gy in 25 fractions over 5 weeks was compared with 41·6 Gy or 39 Gy in 13 fractions over 5 weeks. In START-B, a regimen of 50 Gy in 25 fractions over 5 weeks was compared with 40 Gy in 15 fractions over 3 weeks. Eligibility criteria included age older than 18 years and no immediate surgical reconstruction. Primary endpoints were local-regional tumour relapse and late normal tissue effects. Analysis was by intention to treat. Follow-up data are still being collected. This study is registered as an International Standard Randomised Controlled Trial, number ISRCTN59368779. FINDINGS: START-A enrolled 2236 women. Median follow-up was 9·3 years (IQR 8·0-10·0), after which 139 local-regional relapses had occurred. 10-year rates of local-regional relapse did not differ significantly between the 41·6 Gy and 50 Gy regimen groups (6·3%, 95% CI 4·7-8·5 vs 7·4%, 5·5-10·0; hazard ratio [HR] 0·91, 95% CI 0·59-1·38; p=0·65) or the 39 Gy (8·8%, 95% CI 6·7-11·4) and 50 Gy regimen groups (HR 1·18, 95% CI 0·79-1·76; p=0·41). In START-A, moderate or marked breast induration, telangiectasia, and breast oedema were significantly less common normal tissue effects in the 39 Gy group than in the 50 Gy group. Normal tissue effects did not differ significantly between 41·6 Gy and 50 Gy groups. START-B enrolled 2215 women. Median follow-up was 9·9 years (IQR 7·5-10·1), after which 95 local-regional relapses had occurred. The proportion of patients with local-regional relapse at 10 years did not differ significantly between the 40 Gy group (4·3%, 95% CI 3·2-5·9) and the 50 Gy group (5·5%, 95% CI 4·2-7·2; HR 0·77, 95% CI 0·51-1·16; p=0·21). In START-B, breast shrinkage, telangiectasia, and breast oedema were significantly less common normal tissue effects in the 40 Gy group than in the 50 Gy group. INTERPRETATION: Long-term follow-up confirms that appropriately dosed hypofractionated radiotherapy is safe and effective for patients with early breast cancer. The results support the continued use of 40 Gy in 15 fractions, which has already been adopted by most UK centres as the standard of care for women requiring adjuvant radiotherapy for invasive early breast cancer. FUNDING: Cancer Research UK, UK Medical Research Council, UK Department of Health.
Assuntos
Neoplasias da Mama/radioterapia , Fracionamento da Dose de Radiação , Recidiva Local de Neoplasia/radioterapia , Guias de Prática Clínica como Assunto/normas , Adulto , Idoso , Idoso de 80 Anos ou mais , Antineoplásicos/uso terapêutico , Neoplasias da Mama/mortalidade , Neoplasias da Mama/terapia , Terapia Combinada , Feminino , Seguimentos , Humanos , Mastectomia , Mastectomia Segmentar , Pessoa de Meia-Idade , Invasividade Neoplásica , Recidiva Local de Neoplasia/mortalidade , Recidiva Local de Neoplasia/terapia , Estadiamento de Neoplasias , Prognóstico , Radioterapia Adjuvante , Padrões de Referência , Taxa de SobrevidaRESUMO
Previous studies from our laboratory have identified a link between intracellular topoisomerase IIα (topo IIα) levels and chromosomal radiosensitivity, as measured by the frequencies of chromatid breaks in the so-called G2-assay. Lower topo IIα levels were associated with reduced chromosomal radiosensitivity in cultured human cells. These findings supported a model, in which it is proposed that such chromatid breaks are the result of radiation-induced errors made by topoisomerase IIα during decatenation of chromatids. Studies from our and other laboratories, using the G2-assay, have shown that phytohaemagglutinin (PHA)-stimulated peripheral blood T-lymphocytes from 40% of female breast cancer cases show elevated chromatid break frequencies when exposed to a small standard dose of ionizing radiation, i.e. elevated above the 90th percentile of a group of female control samples. In the present study we have used a modified G2-assay to test whether elevated frequency of chromatid breaks in breast cancer cases is linked with elevated intracellular topo IIα level in PHA-stimulated T-lymphocytes, and also whether there is a general correlation between chromosomal radiosensitivity and topo IIα level. Our results confirm previous studies that 40% of breast cancer cases show elevated radiosensitivity as compared with controls. Also, the mean chromatid break frequency in breast cancer cases was significantly higher than in controls (P = 0.0001). We found that the mean topo IIα level in the cohort of breast cancer cases studied was significantly raised, as compared with controls (P = 0.0016), which could indicate a genetic propensity towards a raised intracellular production of topo IIα in these individuals. There was no direct correlation between chromosomal radiosensitivity and topo IIα level for individual samples either in the breast cancer cohort or in controls. However, a comparison between control and breast cancer samples shows a higher mean topo IIα level in breast cancer samples that correlates with the elevated mean chromatid break frequency seen in these patient samples. We found no meaningful correlations between either chromatid break frequency or topo IIα level and either tumour grade or hormone status. We conclude that elevated intracellular topo IIα level is likely to be a significant factor in determining the chromosomal response of stimulated T-lymphocytes from certain breast cancer cases.
Assuntos
Antígenos de Neoplasias/análise , Neoplasias da Mama/genética , Dano ao DNA , DNA Topoisomerases Tipo II/análise , Proteínas de Ligação a DNA/análise , Tolerância a Radiação/genética , Linfócitos T/efeitos da radiação , Adulto , Idoso , Idoso de 80 Anos ou mais , Neoplasias da Mama/patologia , Estudos de Casos e Controles , Linhagem Celular Tumoral , Cromátides/genética , Cromossomos Humanos , Feminino , Humanos , Pessoa de Meia-Idade , Radiação Ionizante , Linfócitos T/metabolismoRESUMO
Metformin may reduce the incidence of breast cancer and enhance response to neoadjuvant chemotherapy in diabetic women. This trial examined the effects of metformin on Ki67 and gene expression in primary breast cancer. Non-diabetic women with operable invasive breast cancer received pre-operative metformin. A pilot cohort of eight patients had core biopsy of the cancer at presentation, a week later (without treatment; internal control), then following metformin 500-mg o.d. for 1 week increased to 1-g b.d. for a further week continued to surgery. A further 47 patients had core biopsy at diagnosis were randomized to metformin (the same dose regimen) or no drug, and 2 weeks later had core biopsy at surgery. Ki67 immunohistochemistry, transcriptome analysis on formalin-fixed paraffin-embedded cores and serum insulin determination were performed blinded to treatment. Seven patients (7/32, 21.9%) receiving metformin withdrew because of gastrointestinal upset. The mean percentage of cells staining for Ki67 fell significantly following metformin treatment in both the pilot cohort (P = 0.041, paired t-test) and in the metformin arm (P = 0.027, Wilcoxon rank test) but was unchanged in the internal control or metformin control arms. Messenger RNA expression was significantly downregulated by metformin for PDE3B (phosphodiesterase 3B, cGMP-inhibited; a critical regulator of cAMP levels that affect activation of AMP-activated protein kinase, AMPK), confirmed by immunohistochemistry, SSR3, TP53 and CCDC14. By ingenuity pathway analysis, the tumour necrosis factor receptor 1 (TNFR1) signaling pathway was most affected by metformin: TGFB and MEKK were upregulated and cdc42 downregulated; mTOR and AMPK pathways were also affected. Gene set analysis additionally revealed that p53, BRCA1 and cell cycle pathways also had reduced expression following metformin. Mean serum insulin remained stable in patients receiving metformin but rose in control patients. This trial presents biomarker evidence for anti-proliferative effects of metformin in women with breast cancer and provides support for therapeutic trials of metformin.
Assuntos
Neoplasias da Mama/tratamento farmacológico , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Hipoglicemiantes/farmacologia , Hipoglicemiantes/uso terapêutico , Metformina/farmacologia , Metformina/uso terapêutico , Adulto , Idoso , Idoso de 80 Anos ou mais , Neoplasias da Mama/genética , Neoplasias da Mama/metabolismo , Nucleotídeo Cíclico Fosfodiesterase do Tipo 3/genética , Feminino , Perfilação da Expressão Gênica , Humanos , Insulina/sangue , Antígeno Ki-67/metabolismo , Pessoa de Meia-Idade , Reprodutibilidade dos Testes , Transdução de Sinais/genética , Proteína Supressora de Tumor p53/genéticaRESUMO
INTRODUCTION: Immunohistochemistry of primary breast cancer is routinely used to guide changes in therapy at the time of relapse. Retrospective reviews suggest that the estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor type 2 (HER2) receptor may differ between the primary and loco-regional recurrence or distant metastases. The Breast Recurrence In Tissues Study (BRITS) was a large, multicentre, prospective study to examine changes in ER, PR and HER2. METHODS: Matched primary and recurrent breast cancer tissue samples were prospectively collected from 205 women attending 20 institutions. Central laboratory immunohistochemical analysis of core biopsies and tissue microarrays of ER and PR using the Allred and Quickscore methods and HER2 (confirmed by fluorescence in situ hybridisation (FISH) for HER2 2+) were performed. RESULTS: From 205 consenting women, 18 (8.8%) did not have recurrent disease on biopsy, 35 were ineligible, 13 had insufficient paired tissue and 2 were excluded for safety reasons. Paired samples from 137 women, mean age 62.6 years (range 27-87 years), 83/137 (60.6%) postmenopausal with a median 92.2 months (range 5-327 months) from primary to recurrence and 88 (64.2%) as locoregional recurrence were successfully analysed. A switch in receptor status, in either direction, by Allred score, was identified for ER in 14 patients (10.2%; P = 0.983 Wilcoxon sign rank test), PR in 34 (24.8%; P = 0.003 Wilcoxon sign rank test) and HER2 in 4 (2.9%; P = 0.074 Wilcoxon sign rank test). There was no difference between locoregional or distant recurrence in the proportion who switched. The switch in receptor status led to a change in the subsequent treatment plan for 24 patients (17.5%). CONCLUSIONS: This prospective study confirms retrospective evidence that the management of relapsed breast cancer should include confirmatory tissue sampling and identify switches of ER, PR or HER2 which change therapeutic management for one in six patients.
Assuntos
Neoplasias da Mama , Recidiva Local de Neoplasia , Receptor ErbB-2/análise , Receptores de Estrogênio/análise , Receptores de Progesterona/análise , Adulto , Idoso , Idoso de 80 Anos ou mais , Biomarcadores Tumorais/análise , Biomarcadores Tumorais/genética , Neoplasias da Mama/diagnóstico , Neoplasias da Mama/metabolismo , Neoplasias da Mama/patologia , Feminino , Expressão Gênica , Humanos , Hibridização in Situ Fluorescente , Pessoa de Meia-Idade , Pós-Menopausa , Estudos Prospectivos , Receptor ErbB-2/genética , Receptor ErbB-2/metabolismo , Receptores de Estrogênio/genética , Receptores de Progesterona/genética , Estatísticas não ParamétricasRESUMO
AIMS AND OBJECTIVES: To evaluate a nurse-led clinic for patients undergoing radiotherapy to the head and neck. BACKGROUND: The side effects of radiotherapy to the head and neck are superimposed on already significant physical and psychological morbidity. Medical review clinics tend to focus on treatment complications and there is evidence that specialist nurses can provide more holistic care for patients. However, doubts have been raised about the appropriateness of nurse-led review in this highly symptomatic and complex group. DESIGN: This evaluation compared medical on-treatment review (Phase 1) with a nurse-led clinic (Phase 2) for patients having radiotherapy to the head and neck, using an historical control group. METHODS: Twenty patients were reviewed by their consultant and 23 by a nurse specialist, using a clinic protocol. A mixed-method approach to data collection was taken. Patients completed weekly quality of life questionnaires and were asked about their experiences of support and care. General practitioners completed a questionnaire about the communication received from the clinic. Checklists assessed the content of clinic consultations. RESULTS: Patients valued the relationship developed with the nurse specialist, had longer, more frequent consultations and were more often referred to the multidisciplinary team. The nurse specialist managed 83% of consultations without referral to the consultant. Few significant differences in quality of life were found between the groups. There were indications that oral and nutritional problems were managed more effectively in the nurse-led clinic, although emotional functioning was higher in the medical group. GPs were positive about the timing and content of information received. CONCLUSIONS: On-treatment review for patients with head and neck cancer can be effectively managed by a nurse specialist. Relevance to Practice. Radiotherapy nurse specialists make an important contribution to the supportive care of patients with head and neck cancer. More investment is required to maximize their contribution.
Assuntos
Atitude Frente a Saúde , Neoplasias de Cabeça e Pescoço , Enfermeiros Clínicos/organização & administração , Enfermagem Oncológica/organização & administração , Radioterapia (Especialidade)/organização & administração , Atividades Cotidianas/psicologia , Idoso , Assistência Ambulatorial/organização & administração , Assistência Ambulatorial/psicologia , Feminino , Neoplasias de Cabeça e Pescoço/enfermagem , Neoplasias de Cabeça e Pescoço/psicologia , Neoplasias de Cabeça e Pescoço/radioterapia , Saúde Holística , Humanos , Modelos Lineares , Masculino , Pessoa de Meia-Idade , Enfermeiros Clínicos/psicologia , Papel do Profissional de Enfermagem/psicologia , Avaliação em Enfermagem , Pesquisa em Avaliação de Enfermagem , Pesquisa Metodológica em Enfermagem , Qualidade de Vida/psicologia , Radioterapia/efeitos adversos , Radioterapia/enfermagem , Radioterapia/psicologia , Escócia , Inquéritos e QuestionáriosRESUMO
One of the concerns of using sentinel node biopsy (SNB) is the risks of a false-negative result (FNR). We have created a mathematical model to estimate the effects of FNR on mortality because of excess local recurrence and adjuvant therapy inappropriately withheld. With a FNR of 9.7%, the absolute effect on 10-year mortality is estimated to be less than 0.6% for all patients with tumours <2 cm in size. Since the impact of FNR on mortality is small and FNR rates do not improve with training, we suggest that detection rate alone is an adequate criterion for judging competence in SNB.
Assuntos
Neoplasias da Mama/patologia , Reações Falso-Negativas , Biópsia de Linfonodo Sentinela/métodos , Neoplasias da Mama/mortalidade , Feminino , Humanos , Modelos Biológicos , Reprodutibilidade dos Testes , Análise de SobrevidaRESUMO
PURPOSE: To compare overall survival (OS) for fulvestrant 500 mg versus anastrozole as first-line endocrine therapy for advanced breast cancer. PATIENTS AND METHODS: The Fulvestrant First-Line Study Comparing Endocrine Treatments (FIRST) was a phase II, randomized, open-label, multicenter trial. Postmenopausal women with estrogen receptor-positive, locally advanced/metastatic breast cancer who had no previous therapy for advanced disease received either fulvestrant 500 mg (days 0, 14, 28, and every 28 days thereafter) or anastrozole 1 mg (daily). The primary end point (clinical benefit rate [72.5% and 67.0%]) and a follow-up analysis (median time to progression [23.4 months and 13.1 months]) have been reported previously for fulvestrant 500 mg and anastrozole, respectively. Subsequently, the protocol was amended to assess OS by unadjusted log-rank test after approximately 65% of patients had died. Treatment effect on OS across several subgroups was examined. Tolerability was evaluated by adverse event monitoring. RESULTS: In total, 205 patients were randomly assigned (fulvestrant 500 mg, n = 102; anastrozole, n = 103). At data cutoff, 61.8% (fulvestrant 500 mg, n = 63) and 71.8% (anastrozole, n = 74) had died. The hazard ratio (95% CI) for OS with fulvestrant 500 mg versus anastrozole was 0.70 (0.50 to 0.98; P = .04; median OS, 54.1 months v 48.4 months). Treatment effects seemed generally consistent across the subgroups analyzed. No new safety issues were observed. CONCLUSION: There are several limitations of this OS analysis, including that it was not planned in the original protocol but instead was added after time-to-progression results were analyzed, and that not all patients participated in additional OS follow-up. However, the present results suggest fulvestrant 500 mg extends OS versus anastrozole. This finding now awaits prospective confirmation in the larger phase III FALCON (Fulvestrant and Anastrozole Compared in Hormonal Therapy Naïve Advanced Breast Cancer) trial (ClinicalTrials.gov identifier: NCT01602380).
Assuntos
Antineoplásicos Hormonais/administração & dosagem , Inibidores da Aromatase/administração & dosagem , Neoplasias da Mama/tratamento farmacológico , Neoplasias da Mama/patologia , Estradiol/análogos & derivados , Antagonistas do Receptor de Estrogênio/administração & dosagem , Nitrilas/administração & dosagem , Triazóis/administração & dosagem , Adulto , Idoso , Anastrozol , Intervalo Livre de Doença , Esquema de Medicação , Estradiol/administração & dosagem , Feminino , Fulvestranto , Humanos , Estimativa de Kaplan-Meier , Pessoa de Meia-Idade , Resultado do TratamentoRESUMO
BACKGROUND: Different jurisdictions report different breast cancer treatment rates. Evidence-based optimal utilization models may be specific to the derived population. We compared predicted optimal with actual endocrine and chemotherapy utilization in British Columbia, Canada; Dundee, Scotland; and Perth, Western Australia. DESIGN: Data were analyzed for differences in demography, tumour, and treatment. Epidemiological data were fitted to published Australian optimal radiotherapy utilization trees and region-specific optimal treatment rates were calculated. Optimal and actual systemic therapy rates from 2 population-based and 1 institution-based cancer registries were compared for patients diagnosed with breast cancer between 2000-2004, and 2002 for British Columbia. RESULTS: Chemotherapy rates differed between British Columbia (32%), Perth (29%), and Dundee (24%, p = 0.014). Endocrine therapy rates were similar between British Columbia (56%), Perth (59%), and Dundee (64%, p > 0.05). Actual utilization rates were lower than optimal estimates for chemotherapy, but higher for endocrine therapy. Region-specific optimal utilization rates at diagnosis varied between 50-56% for chemotherapy, and 49-54% for endocrine therapy. Variation was attributed to local differences in demographics, and tumour stage. CONCLUSION: Actual treatment rates varied. There was lower than estimated optimal chemotherapy use but higher than expected use of endocrine therapy.
Assuntos
Antineoplásicos/uso terapêutico , Neoplasias da Mama/tratamento farmacológico , Uso de Medicamentos/estatística & dados numéricos , Fidelidade a Diretrizes/estatística & dados numéricos , Padrões de Prática Médica/estatística & dados numéricos , Adulto , Idoso , Idoso de 80 Anos ou mais , Antineoplásicos Hormonais/uso terapêutico , Colúmbia Britânica , Uso de Medicamentos/normas , Medicina Baseada em Evidências , Feminino , Pesquisas sobre Atenção à Saúde , Humanos , Modelos Logísticos , Pessoa de Meia-Idade , Modelos Teóricos , Guias de Prática Clínica como Assunto , Sistema de Registros , Escócia , Austrália OcidentalRESUMO
Radiotherapy is a key treatment option for breast cancer, yet the molecular responses of normal human breast epithelial cells to ionizing radiation are unclear. A murine subcutaneous xenograft model was developed in which nonneoplastic human breast tissue was maintained with the preservation of normal tissue architecture, allowing us to study for the first time the radiation response of normal human breast tissue in situ. Ionizing radiation induced dose-dependent p53 stabilization and p53 phosphorylation, together with the induction of p21(CDKN1A) and apoptosis of normal breast epithelium. Although p53 was stabilized in both luminal and basal cells, induction of Ser392-phosphorylated p53 and p21 was higher in basal cells and varied along the length of the ductal system. Basal breast epithelial cells expressed ΔNp63, which was unchanged on irradiation. Although stromal responses themselves were minimal, the response of normal breast epithelium to ionizing radiation differed according to the stromal setting. We also demonstrated a dose-dependent induction of γ-H2AX foci in epithelial cells that was similarly dependent on the stromal environment and differed between basal and luminal epithelial cells. The intrinsic differences between human mammary cell types in response to in vivo irradiation are consistent with clinical observation that therapeutic ionizing radiation is associated with the development of basal-type breast carcinomas. Furthermore, there may be clinically important stromal-epithelial interactions that influence DNA damage responses in the normal breast. These findings demonstrate highly complex responses of normal human breast epithelium following ionizing radiation exposure and emphasize the importance of studying whole-tissue effects rather than single-cell systems.