Abemaciclib plus a nonsteroidal aromatase inhibitor as initial therapy for HR+, HER2- advanced breast cancer: final overall survival results of MONARCH 3.

BACKGROUND: In MONARCH 2, the addition of abemaciclib to fulvestrant significantly improved both progression-free survival (PFS) and overall survival (OS) in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC) with disease progression on prior endocrine therapy. In MONARCH 3, the addition of abemaciclib to a nonsteroidal aromatase inhibitor (NSAI) as initial therapy for HR+, HER2- ABC significantly improved PFS. Here, we present the prespecified final OS results for MONARCH 3. PATIENTS AND METHODS: MONARCH 3 is a randomized, double-blind, phase III study of abemaciclib plus NSAI (anastrozole or letrozole) versus placebo plus NSAI in postmenopausal women with HR+, HER2- ABC without prior systemic therapy in the advanced setting. The primary objective was investigator-assessed PFS; OS was a gated secondary endpoint, and chemotherapy-free survival was an exploratory endpoint. RESULTS: A total of 493 women were randomized 2 : 1 to receive abemaciclib plus NSAI (n = 328) or placebo plus NSAI (n = 165). After a median follow-up of 8.1 years, there were 198 OS events (60.4%) in the abemaciclib arm and 116 (70.3%) in the placebo arm (hazard ratio, 0.804; 95% confidence interval 0.637-1.015; P = 0.0664, non-significant). Median OS was 66.8 versus 53.7 months for abemaciclib versus placebo. In the subgroup with visceral disease, there were 113 OS events (65.3%) in the abemaciclib arm and 65 (72.2%) in the placebo arm (hazard ratio, 0.758; 95% confidence interval 0.558-1.030; P = 0.0757, non-significant). Median OS was 63.7 months versus 48.8 months for abemaciclib versus placebo. The previously demonstrated PFS benefit was sustained, and chemotherapy-free survival numerically improved with the addition of abemaciclib. No new safety signals were observed. CONCLUSIONS: Abemaciclib combined with an NSAI resulted in clinically meaningful improvement in median OS (intent-to-treat population: 13.1 months; subgroup with visceral disease: 14.9 months) in patients with HR+ HER2- ABC; however, statistical significance was not reached.

Adjuvant abemaciclib combined with endocrine therapy for high-risk early breast cancer: safety and patient-reported outcomes from the monarchE study.

BACKGROUND: In monarchE, abemaciclib plus endocrine therapy (ET) as adjuvant treatment of hormone receptor-positive, human epidermal growth factor 2-negative, high-risk, early breast cancer (EBC) demonstrated a clinically meaningful improvement in invasive disease-free survival versus ET alone. Detailed safety analyses conducted at a median follow-up of 27 months and key patient-reported outcomes (PROs) are presented. PATIENTS AND METHODS: The safety population included all patients who received at least one dose of study treatment (n = 5591). Safety analyses included incidence, management, and outcomes of common and clinically relevant adverse events (AEs). Patient-reported health-related quality of life, ET symptoms, fatigue, and side-effect burden were assessed. RESULTS: The addition of abemaciclib to ET resulted in higher incidence of grade ≥3 AEs (49.7% versus 16.3% with ET alone), predominantly laboratory cytopenias [e.g. neutropenia (19.6%)] without clinical complications. Abemaciclib-treated patients experienced more serious AEs (15.2% versus 8.8%). Discontinuation of abemaciclib and/or ET due to AEs occurred in 18.5% of patients, mainly due to grade 1/2 AEs (66.8%). AEs were managed with comedications (e.g. antidiarrheals), abemaciclib dose holds (61.7%), and/or dose reductions (43.4%). Diarrhea was generally low grade (grade 1/2: 76%); grade 2/3 events were highest in the first month (20.5%), most were short-lived (≤7 days) and did not recur. Venous thromboembolic events (VTEs) were higher with abemaciclib + ET (2.5%) versus ET (0.6%); in the abemaciclib arm, increased VTE risk was observed with tamoxifen versus aromatase inhibitors (4.3% versus 1.8%). PROs were similar between arms, including being 'bothered by side-effects of treatment', except for diarrhea. At ≥3 months, most patients reporting diarrhea reported 'a little bit' or 'somewhat'. CONCLUSIONS: In patients with high-risk EBC, adjuvant abemaciclib + ET has an acceptable safety profile and tolerability is supported by PRO findings. Most AEs were reversible and manageable with comedications and/or dose modifications, consistent with the known abemaciclib toxicity profile.

Adjuvant abemaciclib combined with endocrine therapy for high-risk early breast cancer: updated efficacy and Ki-67 analysis from the monarchE study.

BACKGROUND: Adjuvant abemaciclib combined with endocrine therapy (ET) previously demonstrated clinically meaningful improvement in invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) in hormone receptor-positive, human epidermal growth factor receptor 2-negative, node-positive, high-risk early breast cancer at the second interim analysis, however follow-up was limited. Here, we present results of the prespecified primary outcome analysis and an additional follow-up analysis. PATIENTS AND METHODS: This global, phase III, open-label trial randomized (1 : 1) 5637 patients to adjuvant ET for ≥5 years ± abemaciclib for 2 years. Cohort 1 enrolled patients with ≥4 positive axillary lymph nodes (ALNs), or 1-3 positive ALNs and either grade 3 disease or tumor ≥5 cm. Cohort 2 enrolled patients with 1-3 positive ALNs and centrally determined high Ki-67 index (≥20%). The primary endpoint was IDFS in the intent-to-treat population (cohorts 1 and 2). Secondary endpoints were IDFS in patients with high Ki-67, DRFS, overall survival, and safety. RESULTS: At the primary outcome analysis, with 19 months median follow-up time, abemaciclib + ET resulted in a 29% reduction in the risk of developing an IDFS event [hazard ratio (HR) = 0.71, 95% confidence interval (CI) 0.58-0.87; nominal P = 0.0009]. At the additional follow-up analysis, with 27 months median follow-up and 90% of patients off treatment, IDFS (HR = 0.70, 95% CI 0.59-0.82; nominal P < 0.0001) and DRFS (HR = 0.69, 95% CI 0.57-0.83; nominal P < 0.0001) benefit was maintained. The absolute improvements in 3-year IDFS and DRFS rates were 5.4% and 4.2%, respectively. Whereas Ki-67 index was prognostic, abemaciclib benefit was consistent regardless of Ki-67 index. Safety data were consistent with the known abemaciclib risk profile. CONCLUSION: Abemaciclib + ET significantly improved IDFS in patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative, node-positive, high-risk early breast cancer, with an acceptable safety profile. Ki-67 index was prognostic, but abemaciclib benefit was observed regardless of Ki-67 index. Overall, the robust treatment benefit of abemaciclib extended beyond the 2-year treatment period.

Relationship between IHC4 score and response to neo-adjuvant chemotherapy in estrogen receptor-positive breast cancer.

AIMS: To determine whether IHC4 score assessed on pre-treatment core biopsies (i) predicts response to neo-adjuvant chemotherapy in ER-positive (ER+) breast cancer; (ii) provides more predictive information than Ki67 alone. METHODS: 113 patients with ER+ primary breast cancer treated with neo-adjuvant chemotherapy at the Royal Marsden Hospital between 2002 and 2010 were included in the study. Pathologic assessment of the excision specimen was made for residual disease. IHC4 was determined on pre-treatment core biopsies, blinded to clinical outcome, by immunohistochemistry using quantitative scoring of ER (H-score), PgR (%) and Ki67 (%). Determination of HER2 status was made by immunohistochemistry and fluorescent in situ hybridization for 2+ cases. IHC4 and Ki67 scores were tested for their association with pathological complete response (pCR) rate and residual cancer burden (RCB) score. RESULTS: 18 (16%) of the 113 patients and 8 (9%) of the 88 HER2-ve cases achieved pCR. Ki67 and IHC4 score were both positively associated with achievement of pCR (P < 10-7 and P < 10-9, respectively) and RCB0+1 (P < 10-5 and P < 10-9, respectively) following neo-adjuvant chemotherapy in all patients. Rates of pCR+RCB1 were 45 and 66% in the highest quartiles of Ki67 and IHC4 scores, respectively. In ER+HER2-ve cases, pCR+RCB1 rates were 35% and in the highest quartile of both Ki67 and IHC4. There were no pCRs in the lower half of IHC4 or Ki67 scores. CONCLUSIONS: IHC4 was strongly predictive of pCR or near pCR in ER+ breast cancers following neo-adjuvant chemotherapy. Ki67 was an important component of this predictive ability, but was not as predictive as IHC4.

Residual proliferative cancer burden to predict long-term outcome following neoadjuvant chemotherapy.

BACKGROUND: The purpose of this study was (i) to test the hypothesis that combining Ki67 with residual cancer burden (RCB) following neoadjuvant chemotherapy, as the residual proliferative cancer burden (RPCB), provides significantly more prognostic information than either alone; (ii) to determine whether also integrating information on ER and grade improves prognostic power. PATIENTS AND METHODS: A total of 220 patients treated with neoadjuvant chemotherapy for primary breast cancer were included in the study. Analyses employed a Cox proportional hazard model. Prognostic indices (PIs) were created adding in Ki67, grade and ER to RCB. Leave-one-out cross-validation was used to reduce bias. The overall change in χ(2) of the best model for each index was used to compare the prognostic ability of the different indices. RESULTS: All PIs provided significant prognostic information for patients with residual disease following neoadjuvant chemotherapy. RPCB (χ(2) = 61.4) was significantly more prognostic than either RCB (χ(2) = 38.1) or Ki67 (χ(2) = 53.8) alone P < 0.001. A PI incorporating RCB, Ki67 grade and ER provided the most prognostic information overall and gave χ(2) = 73.8. CONCLUSIONS: This study provides proof of principle that the addition of post-treatment Ki67 to RCB improves the prediction of long-term outcome. Prediction may be further improved by addition of post-treatment grade and ER and warrants further investigation for estimating post-neoadjuvant risk of recurrence. These indices may have utility in stratifying patients for novel therapeutic interventions after neoadjuvant chemotherapy.

Extreme chromosomal instability forecasts improved outcome in ER-negative breast cancer: a prospective validation cohort study from the TACT trial.

BACKGROUND: Chromosomal instability (CIN) has been shown to be associated with drug resistance and poor clinical outcome in several cancer types. However, in oestrogen receptor (ER)-negative breast cancer we have previously demonstrated that extreme CIN is associated with improved clinical outcome, consistent with a negative impact of CIN on tumour fitness and growth. The aim of this current study was to validate this finding using previously defined CIN thresholds in a much larger prospective cohort from a randomised, controlled, clinical trial. PATIENTS AND METHODS: As a surrogate measurement of CIN, dual centromeric fluorescence in situ hybridisation was performed for both chromosomes 2 and 15 on 1173 tumours from the breast cancer TACT trial (CRUK01/001). Each tumour was scored manually and the mean percentage of cells deviating from the modal centromere number was used to define four CIN groups (MCD1-4), where tumours in the MCD4 group were defined as having extreme CIN. RESULTS: In a multivariate analysis of disease-free survival, with a median follow-up of 91 months, increasing CIN was associated with improved outcome in patients with ER-negative cancer (P trend = 0.03). A similar pattern was seen in ER-negative/HER2-negative cancers (Ptrend = 0.007). CONCLUSIONS: This prospective validation cohort study further substantiated the association between extreme CIN and improved outcome in ER-negative breast cancers. Identifying such patients with extreme CIN may help distinguish good from poor prognostic groups, and therefore support treatment and risk stratification in this aggressive breast cancer subtype.

Positron emission tomography/computed tomography in the management of recurrent/metastatic breast cancer: a large retrospective study from the Royal Marsden Hospital.

BACKGROUND: Despite the increasing use of positron emission tomography/computed tomography (PET/CT) in the management of patients with breast cancer, its role is yet to be defined. PATIENTS AND METHODS: We reviewed PET/CT scans carried out in breast cancer patients, the indication, concordance/discordance with other imaging and whether their use had altered patient management. RESULTS: PET/CT scans (233) were carried out in 122 patients between July 2004 and October 2008. Indications were as follows: staging (S) (91), response assessment (RA) (87), clarification (C) of findings on other imaging (32) and reassurance (ASS) (23). In the S group, positive scans were helpful in accurately defining the extent of disease and guided localised or systemic treatment. PET/CT was particularly useful for detecting lytic bone metastases. One-third of the scans was carried out for RA. PET/CT allowed early RA and in some cases appropriate discontinuation of ineffective treatment. PET/CT was used effectively for the clarification of indeterminate lesions on CT (18), magnetic resonance imaging (15) and bone scan (13). In the ASS group, all scans were negative. CONCLUSIONS: PET/CT is useful in accurately staging metastatic disease, assessing response to systemic treatment and clarifying equivocation on other imaging. Incorporation of PET/CT in these areas contributes to breast cancer management optimisation.

EGFR/HER2 inhibitor AEE788 increases ER-mediated transcription in HER2/ER-positive breast cancer cells but functions synergistically with endocrine therapy.

BACKGROUND: Cross-talk between receptor tyrosine kinases and the oestrogen receptor (ER) is implicated in resistance to endocrine therapy. We investigated whether AEE788 (a combined inhibitor of EGFR, HER2 and VEGFR) plus tamoxifen or letrozole enhanced the individual anti-tumour effects of these agents. METHODS: Breast cancer cell lines modelling endocrine-resistant and -sensitive disease were engineered to express aromatase (A) and examined using proliferation, western blotting and ER-alpha transcription assays. RESULTS: AEE788 enhanced the anti-proliferative effect of tamoxifen and letrozole in ER(+) cell lines (MCF-7 2A, ZR75.1 A3 and BT474 A3). This associated with an elevated G1 arrest and nuclear accumulation of p27. It is noteworthy that AEE788 alone or in combination with endocrine therapy increased the expression of progesterone receptor (PGR) and TFF1 in BT474 A3 cells. This may indicate a mechanism of resistance to AEE788 in ER(+)/HER2(+) breast cancers. In a ZR75.1 A3 xenograft, AEE788 alone or in combination with tamoxifen provided no further benefit compared with letrozole. However, letrozole plus AEE788 produced a significantly greater inhibition of tumour growth compared with letrozole alone. CONCLUSION: These data suggest that AEE788 plus letrozole in breast cancer overexpressing HER2 may provide superior anti-tumour activity, compared with single agents.

Treatment of HER2-positive metastatic breast cancer with lapatinib and capecitabine in the lapatinib expanded access programme, including efficacy in brain metastases--the UK experience.

BACKGROUND: The global lapatinib expanded access programme provided access to lapatinib combined with capecitabine for women with HER2-positive metastatic breast cancer (MBC) who previously received anthracycline, taxane and trastuzumab. METHODS: Progression-free survival (PFS) and safety data for 356 patients recruited from the United Kingdom are reported. Efficacy was assessed in 162 patients from the five lead centres, including objective tumour response rate (ORR), time to disease progression (TTP) and efficacy in those with central nervous system (CNS) metastases. Correlation of PFS and ORR with previous capecitabine treatment was also documented. RESULTS: Overall, PFS for the 356 UK patients was 21 weeks (95% CI: 17.6-24.7). In the 162 assessable patients, ORR was 21% (95% CI: 15-27%) and median TTP was 22 weeks (95% CI: 17-27). Efficacy was greater in capecitabine-naive patients (ORR 23 vs 16.3%, P=0.008). For 34 patients with CNS metastases, ORR was 21% (95% CI: 9-39%), with evidence of improvement in neurological symptoms, and median TTP was 22 weeks (95% CI: 15-28). CONCLUSIONS: Lapatinib combined with capecitabine is an active treatment option for women with refractory HER2-positive MBC, including those with progressive CNS disease.

Vinorelbine and infusional 5-fluorouracil in anthracycline and taxane pre-treated metastatic breast cancer.

AIMS: To evaluate the efficacy and toxicity of a combination of intravenous vinorelbine and 5-fluorouracil (5-FU) given by continuous infusion in the treatment of metastatic breast cancer previously treated with anthracyclines and taxanes. MATERIALS AND METHODS: Sixty-one patients with metastatic breast cancer were treated with intravenous vinorelbine 30 mg/m2 on days 1 and 8 of each 21-day cycle together with 5-FU 200 mg/m2/day by continuous infusion. All had previously been treated with an anthracycline and 41% had also been previously treated with a taxane. All had normal haematological, renal and hepatic function and all but three had an Eastern Cooperative Oncology Group performance score of 2 or better. RESULTS: The overall response rate by World Health Organization criteria was 46% (28 patients); excluding nine non-evaluable patients gave a response rate of 54%. In patients who had previously been treated with both an anthracycline and a taxane, a response rate of 50% was observed (12 of 24 patients). Severe toxicity was uncommon, as was toxicity attributable to infusional 5-FU. Myelosuppression was rarely severe, but was common and led to delay or dose reduction in 38% of treatments. Eleven patients (18%) were admitted with fever and/or neutropenia and one patient died. The median received dose intensity was vinorelbine 16 mg/m2/week and 5-FU 143 mg/m2/day. CONCLUSIONS: The combination of vinorelbine and infusional 5-FU is active in metastatic breast cancer, including in patients previously treated with an anthracycline and a taxane. Toxicity is generally manageable, but myelosuppression is significant at this dose regimen. Recommended doses for routine clinical use are 5-FU 200 mg/m2/day and intravenous vinorelbine 30 mg/m2 days 1 and 15 on a 28-day cycle.

Clinical efficacy of capecitabine as first-line chemotherapy in metastatic breast cancer--how low can you go?

Sixty-three patients received capecitabine at 1000 mg/m2 twice daily every 2 out of 3 weeks as first-line treatment for advanced disease at our institution. Forty-five patients (71%) had previously received adjuvant or neoadjuvant chemotherapy. The median number of capecitabine cycles administered was 5(1-40). Forty-eight patients had measurable disease with response rate (RR) of 29%. The median time to progression (TTP) was 18(2-122) weeks. Seven patients (11%) had TTP of >1 yr, four of whom received more than 10(24-40) cycles of capecitabine. Thirty-seven percent of patients still needed dose reductions. Our retrospective audit is consistent with a previously published study which used a higher starting dose of capecitabine as first-line chemotherapy. For a subgroup of patients, capecitabine can result in a long TTP with minimal toxicity. The benefit of continuing capecitabine beyond a fixed number of cycles should be investigated further. Schedules using even lower doses of capecitabine for longer periods may also be of interest.

Exon 5 deletion variant estrogen receptor messenger RNA expression in relation to tamoxifen resistance and progesterone receptor/pS2 status in human breast cancer.

The exon 5 deletion splice variant of estrogen receptor (delta 5 ER), which in vitro is constitutively active in the absence of estrogens, may have a role in conferring both tamoxifen resistance and ER-related phenotype in breast cancer. We have investigated the expression of this variant in vivo (at the level of mRNA) in relation to known tamoxifen resistance and expression of the estrogen-regulated genes progesterone receptor (PgR) and pS2. The amount of delta 5 ER mRNA relative to wild type (WT) ER mRNA (% delta 5/WT) was assayed in 70 tamoxifen-resistant and 50 primary breast carcinomas using reverse transcription/PCR. Both WT and delta 5 ER mRNA were detected in the majority of tumors, although delta 5 ER was detected only in the presence of WT ER. Overall no significant difference was seen in % delta 5/WT ER between tamoxifen-resistant and primary control tumors (medians, 13 and 15%, respectively). Tumors in both control and resistant groups which expressed PgR/pS2 in the absence of measurable ER protein (ER- PgR+ and ER- pS2+) had significantly higher delta 5 ER mRNA levels compared with other phenotypes (P < 0.002). This association with ER-/pS2+ tumors has not been demonstrated previously. In ER+ tumors which expressed pS2, significantly greater delta 5 ER mRNA expression was observed in tamoxifen-resistant compared with control tumors (P = 0.05). A similar although nonsignificant trend was observed in ER+ PgR+ tumors. While delta 5 ER mRNA is unlikely to be responsible for tamoxifen resistance in most breast cancers, elevated delta 5 ER mRNA levels may be important in some tumors, especially those which continue to express high levels of PgR/pS2.

Clinical and endocrine effects of the oral aromatase inhibitor vorozole in postmenopausal patients with advanced breast cancer.

Vorozole is an orally active, nonsteroidal aromatase inhibitor. Twenty-four postmenopausal patients with advanced breast cancer who had relapsed after treatment with tamoxifen received three separate daily doses of vorozole (1, 2.5, and 5 mg) each for 1 month in a randomized, double-blind, phase II study. There was significant suppression (P < 0.001) of serum estradiol at all three doses (median reduction, 91, 90, and 89%, respectively). There was a significant trend (P = 0.02) for estradiol to be suppressed below the detection limit of the assay (3 pmol/liter) more frequently with an increasing dose of vorozole; 13, 31, and 40% respectively. Estrone and estrone-sulfate levels were likewise reduced at each dose by 52-55% and 64-69%, respectively. There was no significant effect at any dose on aldosterone, testosterone, androstenedione, 17 alpha-hydroxyprogesterone, or thyroid-stimulating hormone levels. A small reduction in cortisol was seen at the 5 mg dose, although the relevance is unclear given that 17 alpha-hydroxyprogesterone levels did not rise. Eight patients (33%) achieved an objective response (2 complete remission, 6 partial remission) with a median response duration of 13 months. Four patients (17%) achieved disease stabilization for more than 6 months. Patients who had responded previously to tamoxifen were more likely to respond to vorozole. There were no significant clinical side effects and the drug was well tolerated. These data suggest that vorozole is a potent and selective oral aromatase inhibitor for use in postmenopausal breast cancer.

Changes in estrogen receptor, progesterone receptor, and pS2 expression in tamoxifen-resistant human breast cancer.

Changes in estrogen receptor (ER) expression and function may explain the development of tamoxifen resistance in breast cancer. ER expression was measured by an immunohistochemical assay, validated for use in tamoxifen-treated tumors against a biochemical enzyme immunoassay, in 72 paired biopsies taken before treatment and at progression or relapse on tamoxifen. Progesterone receptor (PgR) and pS2 gene expression were also measured immunohistochemically as an indicator of ER function. Overall the frequency of ER expression was reduced from 37 of 72 (51%) pretamoxifen to 21 of 72 (29%) at progression or relapse, with a significant reduction in the quantitative level of ER (P < 0.0001; Wilcoxon signed rank sum test). Tumors treated with primary tamoxifen that responded but then developed acquired resistance frequently remained ER positive (ER+) at relapse: 16 of 18 (89%) were ER+ pretamoxifen (75% of these expressed either PgR or pS2) and 11 of 18 (61%) were ER+ at relapse (82% continued to express PgR or pS2). In contrast, only 3 of 20 (15%) tumors that progressed on primary tamoxifen with de novo resistance were ER+ pretamoxifen, and all tumors were ER- at progression. At progression, 6 of 20 (30%) of these tumors expressed high levels of PgR (mean H-score, 98) and/or pS2 (mean, 50% cells positive), despite being ER-. In tumors that recurred during adjuvant tamoxifen therapy, including locoregional and metastatic lesions, ER expression was significantly reduced from 18 of 34 (53%) in the original primary tumor to 10 of 34 (29%) at relapse (P = 0.002). PgR expression was likewise significantly reduced in this group (P = 0.001). This study confirms that expression of a functional ER in breast cancer is a strong predictor for primary response to tamoxifen. Although ER was reduced in tamoxifen-resistant tumors overall, the development of acquired resistance was associated with maintained ER expression and function in many tumors, whereas de novo resistance remained related to lack of ER expression. Recurrence during adjuvant tamoxifen was associated with development of an ER/PgR-negative phenotype in some tumors. These data imply that separate mechanisms of resistance may occur in these different clinical subgroups.

Comparison of estrogen receptor DNA binding in untreated and acquired antiestrogen-resistant human breast tumors.

Preliminary studies have suggested that measuring the ability of immunoreactive 67-kDa estrogen receptor (ER) to bind DNA and form in vitro complexes with its cognate estrogen response element (ERE) might serve to identify breast tumors most likely to respond to antiestrogens like tamoxifen. Data from two different surveys of untreated primary breast tumors confirmed that only 67% (74 of 111) of ER-positive tumors express a receptor capable of forming ER-ERE complexes by gel-shift assay, with tumors of lower ER content having significantly reduced ER DNA-binding frequency (56%) relative to those of higher ER content (82%; P = 0.007). In contrast to these untreated tumors, a panel of 41 receptor-positive breast tumors excised after acquiring clinical resistance to tamoxifen during either primary (n = 26) or adjuvant therapy (n = 15) showed a significantly greater ER DNA-binding frequency, with nearly 90% capable of forming ER-ERE complexes (P < 0.02). To assess experimentally whether ER DNA-binding function is altered during the development of antiestrogen resistance, nude mouse MCF-7 tumor xenografts were analyzed before and after the acquisition of in vivo resistance to either tamoxifen or a pure steroidal antiestrogen, ICI 182,780. Tamoxifen-resistant MCF-7 tumors retained full expression of 67-kDa DNA-binding ER, and despite a markedly reduced ER content in the ICI 182,780-treated tumors, the expressed ER in these antiestrogen-resistant tumors exhibited full ability to form ER-ERE complexes. These findings indicate that breast tumors with acquired antiestrogen resistance continue to express ER of normal size and DNA-binding ability and suggest that the failure of antiestrogens to arrest tumor growth during emergence of clinical resistance results from an altered gene-regulatory mechanism(s) other than ER-ERE complex formation.

Idoxifene antagonizes estradiol-dependent MCF-7 breast cancer xenograft growth through sustained induction of apoptosis.

Idoxifene is a novel selective estrogen (E2) receptor (ER) modulator that is currently in clinical development for the treatment of breast cancer. Compared to tamoxifen, idoxifene is metabolically more stable, with a higher relative binding affinity for the ER and reduced agonist activity on breast and uterine cells. Idoxifene also inhibits calmodulin, a calcium-binding protein that is involved in cell signal transduction pathways. In this study, the abilities of idoxifene and tamoxifen to antagonize E2-dependent MCF-7 xenograft growth in oophorectomized athymic mice were compared. The basis for idoxifene's antitumor activity was examined by comparing the effectiveness of the clinically used transisomer (referred to here as idoxifene) with its cis-isomer, which has a 50-fold lower relative binding affinity for ER than idoxifene but similar calmodulin-inhibitory activity. Changes in tumor cell proliferation, apoptosis, and ER-dependent protein expression were studied. Both idoxifene and tamoxifen significantly inhibited E2-dependent tumor growth, whereas cis-idoxifene had little effect. Withdrawal of E2 support induced significant tumor regression due to impaired cell proliferation (Ki-67 score, 9 versus 51% compared to E2 controls) and induction of apoptosis (3.6 versus 0.9% compared to E2 controls). Both anti-E2s inhibited cell proliferation and caused a significant 3-fold induction of apoptosis in E2 supported tumors after 1 week, which was maintained for 3 months with idoxifene (3.1 versus 0.48% compared to E2 controls) but decreased back to baseline in tumors treated with tamoxifen (0.69%). In contrast, cis-idoxifene had no effect on either cell proliferation or apoptosis. Both tamoxifen and idoxifene initially induced ER expression, whereas prolonged therapy with tamoxifen significantly reduced progesterone receptor levels. In conclusion, idoxifene resulted in similar inhibition of E2-dependent MCF-7 xenograft growth compared with tamoxifen, an effect that is mediated via ER rather than through calmodulin. Sustained induction of apoptosis may contribute to prolonged antagonism of E2-dependent growth, and it occurred to a greater extent following 3 months of idoxifene, compared to tamoxifen.

Clinical trials of intracellular signal transductions inhibitors for breast cancer--a strategy to overcome endocrine resistance.

Acquired resistance to endocrine therapy in breast cancer is associated with an increase in peptide growth factor signaling that results in cross-talk activation of the estrogen receptor (ER). Small molecule signal transduction inhibitors (STIs) can target components of these intracellular pathways, and may prove effective in anticancer therapy. However, early phase II clinical trials with various STIs as monotherapy in advanced breast cancer have shown only a modest level of efficacy for these intracellular inhibitors. Preclinical data suggest that combinations of tamoxifen with STIs may provide significantly greater growth inhibition than either therapy alone, and, furthermore, may delay the emergence of endocrine resistance. There are now several trials assessing the efficacy of combinations of small molecule tyrosine kinase inhibitors (TKIs), such as gefitinib and lapatinib, with either tamoxifen or aromatase inhibitors both in the second-line, endocrine-resistant and first-line, hormone-sensitive setting. Similar trials continue with both farnesyltransferase inhibitors (FTIs) and mTOR antagonists, where there are strong preclinical data to suggest additive or synergistic effects for either of these agents in combination with endocrine therapies. Biomarker studies in the presurgical setting are also being utilized as an alternative approach to investigate whether combined endocrine/STI therapy is an effective clinical strategy. This article reviews some of the preclinical evidence supporting this strategy, together with the current status of clinical trials in this area.

The anti-oestrogen ICI 182,780, but not tamoxifen, inhibits the growth of MCF-7 breast cancer cells refractory to long-term oestrogen deprivation through down-regulation of oestrogen receptor and IGF signalling.

Long-term culture of MCF-7 wild-type (wt) cells in steroid-depleted medium (LTED) results in hypersensitivity to oestradiol (E2) coinciding with elevated levels of ERalpha and enhanced growth factor signalling. In this study, we aimed to compare the effects of the pure anti-oestrogen ICI 182,780 (ICI) with the competitive anti-oestrogen tamoxifen (TAM) on oestrogen and IGF signalling in these cells. Wt MCF-7 and LTED cells were treated with a log 7 concentration range of E2, TAM or ICI. Effects on cell growth, ERalpha transactivation, expression of ERalpha, ERbeta and components of the IGF pathway were measured with and without insulin. In the presence of insulin, growth of LTED cells was refractory to TAM but inhibited by ICI and E2. In the absence of insulin, LTED cells showed persistent hypersensitivity to E2, and remained inhibited by ICI but were largely unaffected by TAM. ICI but not TAM inhibited ER-mediated gene transcription and treatment with ICI resulted in a dose-dependent reduction in ERalpha levels whilst having no effect on ERbeta expression. IGF-I receptor and insulin receptor substrate 2 levels were increased in LTED versus the Wt MCF-7 cells, and ICI but not TAM reduced their expression in a dose-dependent fashion. Thus IGF signalling as well as ERalpha expression and function are enhanced during LTED. While the resultant cells are resistant to TAM, ICI down-regulates ERalpha, reducing IGF signalling and cell growth. These results support the use of ICI in women with ER-positive breast cancer who have relapsed on an aromatase inhibitor.

Consensus statement. Workshop on therapeutic resistance in breast cancer: impact of growth factor signalling pathways and implications for future treatment.

Anti-hormones (notably tamoxifen), chemotherapy and modern radiotherapeutic approaches are invaluable in the management of breast cancer, and collectively have contributed substantially to the improved survival in this disease. Moreover, there is promise that these successes will continue with the emergence of other endocrine agents (for example, aromatase inhibitors and pure anti-oestrogens). However, de novo and acquired resistance comprises a significant problem with all treatment approaches examined to date. This Workshop aimed to evaluate the contribution made by growth factor signalling pathways in the various resistant states, primarily focusing on resistance to anti-hormonal strategies and spanning experimental models and, where possible, clinical breast cancer data. The successes and limitations of therapeutic targeting of these pathways with various signal transduction inhibitors (STIs) were evaluated in model systems and from emerging clinical trials (including epidermal growth factor receptor inhibitors such as gefitinib). It was concluded that growth factor signalling is an important contributor in the development of endocrine resistance in breast cancer and that use of STIs provides a promising therapeutic strategy for this disease. However, the cancer cell is clearly able to harness alternative growth factor signalling pathways for growth and cell survival in the presence of STI monotherapy and, as a consequence, the efficacy of STIs is likely to be limited by the acquisition of resistance. A number of strategies were proposed from studies in model systems that appeared to enhance anti-tumour actions of existing STI monotherapy, notably including combination therapies targeting multiple pathways. With the increased availability of diverse STIs and improved drug delivery, there is much hope that the more complex therapeutic strategies proposed may ultimately be achievable in clinical practice.