Chemoprevention of breast cancer

Human breast tissue disposition and bioactivity of limonene in women with early-stage breast cancer

Limonene is a bioactive food component found in citrus peel oil that has shown chemopreventive and chemotherapeutic activities in preclinical studies. We conducted an open-label pilot clinical study to determine the human breast tissue disposition of limonene and its associated bioactivity. We recruited 43 women with newly diagnosed operable breast cancer electing to undergo surgical excision to take 2 grams of limonene daily for two to six weeks before surgery. Blood and breast tissue were collected to determine drug/metabolite concentrations and limonene-induced changes in systemic and tissue biomarkers of breast cancer risk or carcinogenesis. Limonene was found to preferentially concentrate in the breast tissue, reaching high tissue concentration (mean = 41.3 μg/g tissue), whereas the major active circulating metabolite, perillic acid, did not concentrate in the breast tissue. Limonene intervention resulted in a 22% reduction in cyclin D1 expression (P = 0.002) in tumor tissue but minimal changes in tissue Ki67 and cleaved caspase-3 expression. No significant changes in serum leptin, adiponectin, TGF-β1, insulin-like growth factor binding protein-3 (IGFBP-3), and interleukin-6 (IL-6) levels were observed following limonene intervention. There was a small but statistically significant postintervention increase in insulin-like growth factor I (IGF-I) levels. We conclude that limonene distributed extensively to human breast tissue and reduced breast tumor cyclin D1 expression that may lead to cell-cycle arrest and reduced cell proliferation. Furthermore, placebo-controlled clinical trials and translational research are warranted to establish limonene's role for breast cancer prevention or treatment.

Acceptability and adherence in a chemoprevention trial among women at increased risk for breast cancer attending the Modena Familial Breast and Ovarian Cancer Center (Italy)

Chemoprevention for women at risk for breast cancer has been shown to be effective, but in actual practice, women's uptake of chemoprevention has been poor. We explored factors that influence acceptability, adherence, and dropout in the International Breast (Prevention) Intervention Study during our first 3 years of activity at the Modena Familial Breast and Ovarian Cancer Center. We evaluated socio-demographic characteristics, health status, adherence, and side effect intensity. Semi-structured interviews analyzed reasons for accepting/refusing/stopping the trial. A total of 471 postmenopausal women were invited to participate, of which 319 declined to participate (68%), 137 accepted to participate (29%), and 15 participants did not make a final decision (3%). Breast cancer-related worries and trust in our preventive and surveillance programs were the most frequent reasons for accepting. Side effect-related worry was the most frequent reason for refusing. General practitioners' and family members' opinions played an important role in the decision-making process. Adherence significantly decreased after a 12-month follow-up, but it remained unchanged after 24- and 36-month follow-ups. Mild/moderate side effects reported by women did not change after 12 months of treatment. Forty percent of women withdrew from the study due to complaints of side effects. We concluded that chemoprevention trials are difficult medical experiments and that the process of deciding about whether or not to participate is based mainly on beliefs and values. This study has important clinical implications. During counselling with prospective participants, it is important to emphasize the potential benefits and to promote an informed choice. How participants make decisions, their belief systems, and their perception of risk are all factors that should be investigated in future research.

Chemoprevention of Breast Cancer: The Paradox of Evidence versus Advocacy Inaction

Women who are at high risk of breast cancer can be offered chemoprevention. Chemoprevention strategies have expanded over the past decade and include selective receptor modulator inhibitors and aromatase inhibitors. Physicians are expected to provide individualized risk assessments to identify high risk women who may be eligible for chemoprevention. It is prudent that physicians utilize a shared decision approach when counseling high risk women about their preventive options. Barriers and misperceptions however exist with patient and physician acceptance of chemoprevention and continue to impede uptake of chemoprevention as a strategy to reduce breast cancer risk. Programs to increase awareness and elucidate the barriers are critical for women to engage in cancer prevention and promote chemoprevention adherence.

Tamoxifen vs Raloxifene vs Exemestane for Chemoprevention

Clinical trial data on selective estrogen receptor modulators (SERMs) and aromatase inhibitors (AIs) have demonstrated reduced breast cancer incidence in the prevention setting among high-risk women. We conducted an extensive review of clinical trials and recent published reports of barriers to uptake of breast cancer chemoprevention, to provide health care professionals with information to improve decision-making regarding chemoprevention. Despite the positive results of these trials, uptake of chemoprevention has been low due to barriers in identifying high-risk women, lack of understanding of risks and benefits, as well as concerns about side effects. Interventions designed to increase uptake have met with limited success. Clinicians can support women in informed decision-making about SERMs and AIs by effectively communicating breast cancer risk and enhancing knowledge about the risks and benefits of chemoprevention. Promoting uptake and adherence to chemoprevention holds promise for reducing the public health burden of this disease.

Weight change associated with anastrozole and tamoxifen treatment in postmenopausal women with or at high risk of developing breast cancer

Weight gain is commonly reported by breast cancer patients on tamoxifen or aromatase inhibitors. Since weight gain may impact on outcome and compliance we have prospectively assessed the effects of these agents on weight change in three randomised trials for the treatment or prevention of breast cancer. Data on weight change in postmenopausal women from three large clinical trials investigating endocrine therapy for the treatment or prevention of breast cancer were analysed (ATAC, IBIS-I and IBIS-II). In the IBIS-I study, mean weight change on tamoxifen was +0.1 kg (SD 0.1) compared with +0.3 kg (SD 0.1) in women taking the placebo (P = 0.3) between baseline and 12 months of follow-up. In the IBIS-II trial, no statistically significant difference was found between anastrozole and placebo after 12 months of follow-up [+0.8 kg (SD 5.3) vs. +0.5 kg (SD 7.4), P = 0.5]. In the ATAC trial, no statistically significant differences in weight gain between anastrozole and tamoxifen were found after 12 months of follow-up [+1.4 kg (SD 3.9) vs. +1.5 kg (SD 4.0), P = 0.4]. Significant baseline predictors for gaining more than 5 kg of weight after 12 months of follow-up were: being younger than 60 years old, smoking and mastectomy. All three trials demonstrate that weight gain occurs primarily within the first 12 months of active treatment in a subset of patients. In the prevention trials, weight gain does not differ between anastrozole, tamoxifen and placebo and also did not differ between anastrozole and tamoxifen in the treatment trial.

Personalized estimates of breast cancer risk in clinical practice and public health

This paper defines absolute risk and some of its properties, and presents applications in breast cancer counseling and prevention. For counseling, estimates of absolute risk give useful perspective and can be used in management decisions that require weighing risks and benefits, such as whether or not to take tamoxifen to prevent breast cancer. Absolute risk models are also useful in designing intervention trials to prevent breast cancer and in assessing the potential reductions in absolute risk of disease that might result from reducing exposures that are associated with breast cancer. In these applications, it is important that the risk model be well calibrated, namely that it accurately predicts the numbers of women who will develop breast cancer in various subsets of the population. Absolute risk models are also needed to implement a 'high risk' prevention strategy that identifies a high-risk subset of the population and focuses intervention efforts on that subset. The limitations of the high-risk strategy are discussed, including the need for risk models with high discriminatory accuracy, and the need for less toxic interventions that can reduce the threshold of risk above which the intervention provides a net benefit. I also discuss the potential use of risk models in allocating prevention resources under cost constraints. High discriminatory accuracy of the risk model, in addition to good calibration, is desirable in this application, and the risk assessment should not be expensive in comparison with the intervention.

Breast cancer prevention trials: large and small trials

Breast cancer is the most common cancer among women in the United States, with 192,870 new cases and 40,170 deaths due to this disease estimated to have occurred 2009. An emphasis on prevention has been increasing in view of a persisting high incidence of disease. Seventy percent of breast cancers are estrogen receptor (ER)-positive, and are therefore presumed to be hormone-responsive and potentially treatable or preventable by anti-estrogenic agents. To date, the large, phase III randomized controlled breast cancer prevention trials have tested and are testing only hormonal drugs designed to antagonize the carcinogenic effect of endogenous estrogen; these agents are either selective estrogen receptor modulators (SERMs) or aromatase inhibitors (AIs). The SERMs, tamoxifen and raloxifene, have been shown in these large trials to reduce the risk of ER-positive breast cancers; prevention trials of AIs are ongoing. Interest is now focusing on developing agents with a broader spectrum of preventive activity, particularly with regard to ER-negative subtypes of breast cancer. A number of phase I and II trials using tissue-derived surrogate endpoint biomarkers (SEBs) as outcomes have been implemented. These smaller trials address prevention not only of ER-negative but also ER-positive breast cancers, since approximately 50% of the latter have been shown to be resistant to the estrogen-targeting drugs used in the large trials. Issues of importance in these smaller trials include choice of agent, selection of appropriate trial participants, trial design, method of access to breast tissue in women without cancer, selection and monitoring of SEBs, and monitoring of drug toxicity.

In vitro cytochrome P450-mediated metabolism of exemestane

Exemestane is a potent and irreversible steroidal aromatase inhibitor drug used for the treatment of estrogen receptor-positive breast cancer. Our aim was to identify and assess the contribution of the specific cytochromes P450 (P450s) responsible for exemestane primary in vitro metabolism. With the use of high-performance liquid chromatography and liquid chromatography-tandem mass spectrometry analytical techniques, 17-hydroexemestane (MI) formation and 6-hydroxymethylexemestane (MII) formation were found to be the predominant exemestane metabolic pathways. In a bank of 15 well characterized human liver microsomes with known P450 isoform-specific activities, the MI formation rate correlated significantly with CYP1A2 (Spearman r = 0.60, p = 0.02) and CYP4A11 (Spearman r = 0.67, p = 0.01) isoform-specific activities, whereas the MII production rate significantly correlated with CYP2B6 (Spearman r = 0.57, p = 0.03) and CYP3A (Spearman r = 0.76, p = 0.005) isoform-specific activities. Recombinant CYP1A1 metabolized exemestane to MI with a catalytic efficiency (Cl(int)) of 150 nl/pmol P450 × min that was at least 3.5-fold higher than those of other P450s investigated. Recombinant CYP3A4 catalyzed MII formation from exemestane with a catalytic efficiency of 840 nl/pmol P450 × min that was at least 4-fold higher than those of other P450s investigated. Among a panel of 10 chemical inhibitors tested, only ketoconazole and troleandomycin (CYP3A-specific chemical inhibitors) significantly inhibited the formation of MII by 45 and 95%, respectively. None of them markedly inhibited the formation of MI. In summary, exemestane seems to be metabolized to MI by multiple P450s that include CYP4A11 and CYP1A1/2, whereas its oxidation to MII is primarily mediated by CYP3A.

Pre-surgical study of the biological effects of the selective cyclo-oxygenase-2 inhibitor celecoxib in patients with primary breast cancer

Cyclo-oxygenase 2 (COX-2) is implicated in the regulation of aromatase transcription in malignant breast tissue and has been considered as a potential target for tissue specific aromatase suppression. We initiated a randomised controlled pre-surgical study of celecoxib versus no treatment in women with primary breast cancer to determine the effects of COX-2 inhibition on markers of biological response. Postmenopausal women (50-80 years of age) with stage I or II, primary breast cancer, were randomised 2:1 to receive 400 mg/day celecoxib or no treatment for 14 days prior to surgery. A core biopsy was obtained pre- and post-treatment. Paired baseline and endpoint biopsies were analysed for Ki67, apoptosis, COX-2, CD31, estrogen receptor (ER) and progesterone receptor (PgR). Comparisons between the treatment groups were conducted using the Mann-Whitney test with a two-sided 5% significance. Of the 25 patients treated, 23 had evaluable data and 19 (83%) were ER positive. Overall the geometric mean change in Ki67, the primary end point, relative to baseline in the celecoxib arm was -16.6% (P = 0.056). The change in the no-treatment group was -8.1% (P = 0.24). There was no statistically significant difference in the change between the two groups. Celecoxib did not significantly affect apoptosis, COX-2, ER or PgR expression. There is only modest evidence for a biological effect of celecoxib in primary breast cancer. However, the trend towards a reduction in Ki67 in ER-positive breast cancer warrants further investigations in a larger cohort of patients.

Effects of anastrozole on cognitive performance in postmenopausal women: a randomised, double-blind chemoprevention trial (IBIS II)

BACKGROUND

Mild cognitive impairments have been recorded in cross-sectional studies of women with breast cancer receiving endocrine treatment. More comprehensive studies were warranted because aromatase inhibitors are being used increasingly in both chemoprevention and adjuvant settings. We report findings from the cognitive subprotocol of the International Breast Intervention Study (IBIS II), a double-blind placebo-controlled trial of anastrozole in postmenopausal women at high risk of developing breast cancer. We aimed to study and compare the effect of anastrozole versus placebo on memory and attention in these women.

METHODS

Between Jan 3, 2003, and Dec 21, 2005, participants were recruited into the cognitive subprotocol from five UK centres. Cognitive assessments were done before randomisation, at 6 months, and at 24 months. 227 of 249 women approached completed a comprehensive set of standardised cognitive tasks at baseline and were randomly assigned to receive anastrozole (1 mg/day for 5 years) or placebo. Psychological morbidity, endocrine symptoms, and self-reported cognitive complaints were also measured. The main outcomes were cognitive task scores at baseline, 6 months, and 24 months. Analyses were done by intention to treat. This study is registered as an International Standard Randomised Controlled Trial, number ISRCTN31488319.

FINDINGS

111 women were assigned to anastrozole and 116 women to placebo. At 6 months, ten women in each group were excluded from analysis, leaving a total of 207 of 227 (91%) women available for further assessments. At 24 months, 24 women were excluded from the anastrozole group and 32 from the placebo group, leaving 151 of 227 (67%) women. We did not note any significant differences between the groups for any of the cognitive tasks. By 6 months, 13 women in both groups reported changes to their memory and this had decreased to five women in the placebo group and three women in the anastrozole group by the 24-month assessment. Significantly more women in the anastrozole group complained of hot flushes at 24 months (23 of 76 [30%] vs 11 of 73 [15%], p=0.032, not corrected for multiple comparison), but this was the only difference in reported endocrine symptoms.

INTERPRETATION

These findings show little or no impairment of cognitive performance with the use of anastrozole compared with placebo in postmenopausal women at high risk of developing breast cancer who were able to tolerate endocrine-related side-effects. Future studies assessing cognition should be done within randomised trials with baseline assessments to ascertain the true extent of the putative effects that treatments for breast cancer might have on memory and attention.

FUNDING

Cancer Research UK, London, UK (grant numbers C6280/A3162 and C6280/A6764).