10515 Background: Adjuvant endocrine prevention reduces the risk of subsequent breast cancer events after ductal carcinoma in situ (DCIS) and precursor lesions, but the toxicity of standard-dose tamoxifen or aromatase inhibitors limits its use. Low-dose tamoxifen (Babytam) has demonstrated a favorable balance of efficacy and tolerability. Whether the magnitude and pattern of benefit vary by menopausal status remains undefined. We performed a pooled analysis of three studies to evaluate Babytam according to menopausal status and type of breast cancer event. Methods: Individual patient data from two randomized trials (Trial 007, JCO 2009; 27:3749; Trial Tam-01, JCO 2023; 41:3116) and one observational study (Int J Cancer 2016; 139:2127) were pooled. Babytam was administered at 5 mg/day (RCTs) or 10 mg every other day (observational). The primary endpoint was recurrence of any breast cancer event, defined as ipsilateral recurrence or new ipsilateral breast cancer, contralateral breast cancer (CBC), distant metastases, or death. Competing risk models were applied for CBC. Multivariable Cox proportional hazards models with study-level random effects were used. Analyses were stratified by menopausal status. Results: A total of 1,772 women were included, 1,568 with DCIS, 101 with ADH, 81 with LCIS, and 21 with pT1a. Babytam significantly reduced overall breast cancer events, with differential effects by menopausal status and event type (table). Reduction in any breast cancer event was driven by a marked decrease in ipsilateral events among postmenopausal women, whereas the preventive effect on CBC was confined to premenopausal women. Few distant metastases or deaths occurred. Conclusions: In this pooled analysis, Babytam significantly reduced breast cancer events following in situ and microinvasive disease, confirming and extending the preventive efficacy observed in TAM-01. Menopausal status was a key modifier of benefit, with ipsilateral risk reduction predominating in postmenopausal women and CBC prevention in premenopausal women. These findings underscore the biological heterogeneity of early breast neoplasia and support Babytam as a risk-adapted, de-escalated endocrine prevention strategy that enables individualized decision-making balancing efficacy, toxicity, and patient characteristics. Clinical trial information: NCT06982313 . Effect of low-dose tamoxifen (babytam) on overall recurrence and contralateral breast cancer by menopausal status. Population Menopausal status Babytam events/N Control events/N HR (95% CI) p-value ER+ Overall 152/678 192/629 0.68 (0.55-0.84) <0.001 Pre 109/366 98/269 0.83 (0.63-1.09) 0.17 Post 40/292 91/354 0.52 (0.36-0.76) <0.001 ER- Overall 7/19 57/225 1.20 (0.54-2.65) 0.65 Considering CBC only All patients Overall 39/812 68/960 0.66 (0.44–1.00) 0.05 Pre 22/457 40/387 0.46 (0.27–0.77) 0.003 Post 16/335 27/560 1.04 (0.55–1.96) 0.89 ER+ Overall 35/678 51/629 0.65 (0.42-0.99) 0.046

Supplementary Table 1: Representativeness of Study Participants

PURPOSE:Tamoxifen 20 mg once-daily reduces the risk of breast cancer recurrence after ductal carcinoma in situ (DCIS), but its use is limited by adverse effects. Lower doses may be effective, but benefit durability and differences according to menopausal status and site of recurrence remain uncertain. METHODS:We conducted an individual-participant pooled analysis of three clinical studies involving women with estrogen receptor-positive or unknown DCIS, microinvasive carcinoma, or high-risk breast lesions. Participants received low-dose tamoxifen (5 mg once daily or 10 mg once-every other day for 2-5 years) or a control intervention. The primary end point was breast cancer-free interval, defined as the first occurrence of any ipsilateral or contralateral invasive breast cancer, DCIS, regional recurrence, or distant recurrence. Hazard ratios (HRs) were estimated with mixed-effects Cox models accounting for between-study variability. RESULTS:Among 1,545 women included with a median follow-up of 9.4 years, low-dose tamoxifen reduced breast cancer events overall, with evidence of treatment heterogeneity according to menopausal status (P = .01). In postmenopausal women, breast cancer events occurred in 40 of 335 receiving low-dose tamoxifen versus 93 of 401 controls (HR, 0.51 [95% CI, 0.35 to 0.73]), with a 10-year absolute reduction of 11.2%. Among premenopausal women, no significant reduction was observed (HR, 0.90 [95% CI, 0.70 to 1.17]), although contralateral breast cancer was reduced (HR, 0.45 [95% CI, 0.26 to 0.76]). Serious adverse events were infrequent and similar between groups. CONCLUSION:Low-dose tamoxifen was associated with a sustained reduction in breast cancer events, with differences by menopausal status and site of event. These findings support endocrine dose de-escalation to improve the benefit-risk profile of preventive therapy in DCIS and high-risk lesions.

10524 Background: Preclinical studies indicate that metformin administered during fasting synergizes with feeding–fasting cycles to suppress tumor growth through activation of the PP2A–GSK3β–MCL1 pathway. The TEAM trial evaluated the feasibility, safety, biological, metabolic, and clinical effects of a short-term metabolic intervention combining prolonged nightly fasting and metformin in operable hormone receptor–positive breast cancer. Methods: TEAM is a randomized, phase IIb, presurgical window-of-opportunity trial. Women with hormone receptor-positive operable invasive breast cancer or DCIS were randomized 1:1 to either ≥16-hour nightly fasting plus metformin 750 mg bid and nutritional counseling (experimental [exp] arm) or to healthy WCRF lifestyle recommendations (control arm). Both groups wore a Continuous Glucose Monitor (CGM) per protocol data downloads. Treatment duration was 4–6 weeks before surgery. The primary endpoint is the absolute change in centrally assessed Ki67 between biopsy and surgery in invasive disease or DCIS. A co-primary endpoint was the difference in post-treatment Ki67 in cancer-adjacent DCIS. Analyses were intention-to-treat. Results: A total of 120 patients were randomized and completed the study (mean±SD, 32±8.6 days). As of December 31, 2025, 105 were evaluable for paired Ki67 analysis due to tissue availability. Since the complete results will be presented at the meeting, current data are descriptive with no inferential statistics and p-values, as per DSMB recommendation. Median baseline Ki67 was 15% in both arms. Median absolute Ki67 change was −3 percentage points (IQR −7 to 1) in the exp arm versus −2 (IQR −4 to 4) in the control arm. The median absolute change in invasive disease was -3 (-7 to 2) versus -1 (-3 to 4), and Ki67 reduction ≥3% occurred in 53% versus 32%, in the exp and control arm, respectively. Post-treatment Ki67 in cancer-adjacent DCIS was 3.5 (2-8.5) vs 4 (2-7). There were 3 pathological CR in the exp arm and 0 in the control arm during the presurgical window. Median weight decreased by 1.75 kg in the exp arm relative to the control arm. Mean tumor 18F-FDG PET SUV decreased by 22% versus 4% in a subgroup of 25 patients with tumors ≥ 15 mm. Reductions were observed in glucose, HOMA-IR, leptin, C-peptide, insulin and IGF-I. Changes in CIP2A and MCL1 were observed in patients with Ki67 reduction. Median adherence to ≥16-hour fasting was 100% (97.4-100); overall metformin adherence was 95% (85%-99%). No dose-limiting toxicities or grade ≥3 hypoglycemia occurred. Conclusions: These preliminary results show that short-term metabolic intervention was feasible, safe, highly compliant, and very inexpensive, and was associated with favorable antiproliferative and metabolic changes that warrant further investigation in breast cancer prevention and treatment. Full results will be presented at the meeting. Clinical trial information: NCT05023967 .

Despite the proven efficacy of tamoxifen in breast cancer prevention, its uptake remains limited due to concerns over side effects. A phase 3 trial showed that low-dose tamoxifen (5 mg/d for 3 years) substantially reduces recurrence with minimal toxicity. After 10 years of follow-up, we observed no clinically significant differences in benign gynecological or breast events between the tamoxifen and placebo arms. The uterus was the most frequently affected site (30 cases per arm), followed by the breast (18 cases) and ovary (5 cases vs 3 cases for tamoxifen and placebo, respectively). Endometrial polyps were similarly distributed. Endometrial thickness remained stable in premenopausal women and showed only a mild, non-clinically significant increase in postmenopausal women on tamoxifen (approximately 1.5 mm). Compared with data on standard-dose tamoxifen, rates of benign events were lower. These findings reinforce the favorable safety profile of low-dose tamoxifen.

Cancer cells exhibit metabolic flexibility between anaerobic glycolysis and oxidative phosphorylation. Preclinical data showed that metformin, an oxidative phosphorylation inhibitor, combined with fasting-induced hypoglycemia led to activation of the PP2A-GSK3ß-Mcl1 axis and inhibition of tumor growth. A window-of-opportunity trial was designed to evaluate the effect of metformin and nightly fasting on proliferation in invasive breast cancer or ductal carcinoma in situ (DCIS). The primary endpoint is the pretreatment/posttreatment change of Ki67 in cancer tissue, and the co-primary endpoint is the difference in posttreatment Ki67 in cancer-adjacent DCIS or high-risk lesions. Participants with hormone receptor-positive invasive breast cancer or DCIS candidates to surgery are being accrued and randomized to either (i) fasting for ≥16 hours nightly, plus nutritional counseling and daily metformin with continuous glucose monitoring, or (ii) continuous glucose monitoring. The intervention lasts 4 to 6 weeks with gradual metformin ramp up to limit gastrointestinal disturbances. The safety of the combination was evaluated as a primary interim endpoint. The frequency of dose-limiting toxicity (≥G3 adverse events related to treatment) was assessed in the first 14 participants in the experimental arm. Most adverse events were of low grade (G1: 50; 90.9%) and unrelated to the treatment (G1: 26 unrelated; 52%). No one discontinued treatment because of toxicity, and no dose-limiting toxicities were observed, so the escalation phase of metformin was significantly shortened from 7 to 3 days. The results of this project will expand knowledge of this prevention approach and possibly provide the basis for large-scale primary prevention studies in at-risk women. PREVENTION RELEVANCE:In a context of rising cancer drug costs, this research explores a low-cost treatment to optimize breast cancer preventive intervention. The approach is safe and based on repurposed drugs that could enhance prevention strategies for obesity- and insulin-related cancers, offering immediate applicability to a large-scale trial in women at risk.

Coffee and tea intake has been suggested to favourably affect survival of cancer patients, but studies published so far produced conflicting results. This systematic review and meta-analysis aimed to summarize the existing evidence on the association between coffee and tea consumption and cancer survival across different types of cancers. We included 26 prospective studies (1993–2023) involving over 40,000 cancer patients from North America, Europe, and Asia. Summary hazard ratios (SHR) comparing high versus low consumption levels were calculated using random effects meta-analysis models for recurrence/progression/death. Overall, a protective effect of coffee and tea consumption on cancer survival was suggested. High coffee and/or tea intake was associated with a 24

BACKGROUND AND AIM:DNA methylation may contribute to a worsening in breast cancer (BC). METHODS:We conducted a matched case-control study to investigate the contribution of DNA methylation (DNAm) in breast cancer recurrence risk. Genome-wide DNAm profiles were generated from peripheral white blood cells (WBC) collected post-surgery from women with primary breast cancer BRCA wild-type, using Illumina Infinium HumanMethylationEPIC array. Cases had to experience recurrence of breast cancer or death and were matched to controls (subjects without recurrence, ratio 1:2) by age at diagnosis (+/- 5 years) and follow-up duration. RESULTS:We identified three differentially methylated regions between the groups. Cases showed two hypomethylated regions, one upstream of the vtRNA2-1 gene (estimate -0.30, p-value < 0.005), and one in the 5' UTR region of the FGFR2 gene (estimate -0.34, p-value < 0.028), whereas one, upstream of the RUFY1 gene (estimate 0.32, p-value < 0.015), was hypermethylated. Additionally, we identified two methylation signals, recognised as predictors of biochemical traits. The chemokine ligand 21 (unadjusted p-value < 0.03) and insulin receptor expression (unadjusted p-value < 0.04) were higher in cases than in controls. CONCLUSIONS:Our exploratory study suggests that specific DNA methylation patterns in WBCs, particularly in genes related to cellular proliferation, invasion, and glucose homeostasis, may be associated with the risk of breast cancer recurrence in BRCA wild-type women. If validated in larger cohorts, these circulating signatures may serve as blood-based biomarkers to improve risk stratification and guide tailored treatment strategies.

Women carrying pathogenic/likely pathogenic (P/LP) variants in moderate- or high-penetrance genes have an increased risk of developing breast cancer. However, most P/LP variants associated with breast cancer risk show incomplete penetrance. Age, gender, family history, polygenic risk, lifestyle, reproductive, hormonal, and environmental factors can affect the expressivity and penetrance of the disease. However, there are gaps in translating how individual genomic variation affects phenotypic presentation. The expansion of criteria for genetic testing and the increasing utilization of comprehensive genetic panels may enhance the identification of individuals carrying P/LP variants linked to hereditary breast cancer. Individualized risk assessment could facilitate the implementation of personalized risk-reduction strategies for these individuals. Preventive interventions encompass lifestyle modifications, chemoprevention, enhanced surveillance through breast imaging, and risk-reducing surgeries. This review addresses the current literature's inconsistencies and limitations, particularly regarding risk factors and the intensity of preventive strategies for women with P/LP variants in moderate- and high-penetrance genes. In addition, it synthesizes the latest evidence on risk assessment and primary and secondary prevention in women at high risk of breast cancer.

TPS10625 Background: Breast cancer (BC) prevention in high-risk women is crucial. Tamoxifen, despite its efficacy, has limited use due to its side effects. Low-dose tamoxifen (LDT) has shown much better balance between BC risk reduction and adverse effects. Additionally, lifestyle interventions (LI) like intermittent caloric restriction (ICR) and physical activity may further reduce BC risk by modulating factors such as mammographic density (MD) and sex hormone-binding globulin (SHBG) levels, which we showed is correlated with reduced breast cancer risk. This study evaluates whether LDT increases circulating SHBG more effectively than LI with or without ICR after six months. Methods: The TOLERANT study is a randomized, four-arm, phase II trial involving 200 high-risk women recruited from four Italian hospitals. Participants will be randomly assigned to one of four intervention arms: (1) LDT, (2) LDT + ICR, (3) LI with step counter, (4) LI with step counter + ICR. Interventions will last six months, and participants' adherence will be monitored through visits, telephone calls and diaries. Eligible women are aged 18-70 with a high risk for BC due to genetic predisposition or a history of intraepithelial neoplasia. Key exclusion criteria include history of invasive BC, BMI <18.5, and certain medical conditions. LDT involves 10 mg tamoxifen every other day. ICR follows a "5:2 diet" model, with five days of normal intake and two days at 25% of regular caloric intake. LI includes personalized advice and step counters targeting 10,000 steps per day. Primary outcome is the change in SHBG levels. Secondary outcomes include changes in metabolic and inflammatory markers, QoL, body composition, microbiome diversity, and MD. Blood and stool samples will be collected at baseline (B), three (3M), and six months (6M) to analyze biomarkers. Body composition will be assessed using bioelectrical impedance analysis, at B, 3M and 6M and MD will be measured in a subset of participants using digital mammography. As of January 20, 2025, a total of 43 participants have been enrolled, including 18 with DCIS and 25 high-risk women. The study, which has received approval from relevant ethics committees, will provide insights into the effectiveness of LDT and LI in reducing BC risk among high-risk women. The results could inform personalized prevention strategies, balancing efficacy with QoL. Trial registration: EuCT number:2023-503994-39-00; Clinical trials.gov NCT06033092 Funding: This work is funded by European Union – Next Generation EU – PNRR M6C2 – Investimento 2.1 Valorizzazione e potenziamento della ricerca biomedica del SSN – Project Code: PNRR-MAD-2022-12376567 - PI Bernardo Bonanni. Co-PI Sara Gandini. The funders had no role in study design, data collection and analysis, or abstract preparation. Reference*: Guerrieri-Gonzaga A et al. PLoS One. 2024 doi journal.pone.0309511. Clinical trial information: NCT06033092 .

Representativeness of Study Participants

Lynch syndrome is a genetic condition predisposing to cancer, particularly colorectal cancer and endometrial cancer, due to germline mutations in MisMatch Repair genes. More rarely, Lynch syndrome is the result of a constitutional MLH1 promoter methylation. This review summarizes the current knowledge about the role of this epigenetic mechanism in the Lynch syndrome. Universal Tumor Screening, performed on tumoral specimens to identify features suggestive of Lynch syndrome, shows the same features both in the case of sporadic cancers and Lynch syndrome-cancers due to a constitutional MLH1 methylation: microsatellite instability, deficiency of MisMatch Repair proteins, and methylation of MLH1 gene. Over the last few years, identifying methylation of MLH1 promoter on tumors was used to discern sporadic tumors from Lynch syndrome tumors: the methylation of the MLH1 promoter was usually explained as a somatic event and this could lead to a missed diagnosis of some Lynch syndrome cases. Therefore, establishing criteria to decide when to test patients for constitutional MLH1 methylation is urgent. In the case of microsatellite instability/deficiency of MisMatch Repair tumors with MLH1 methylation, a germline genetic test could be requested for all colorectal cancer patients aged 55 years or younger and all endometrial cancer patients younger than 50 years old, independently from family history. The prevalence of germline MLH1 epimutations is not precisely known and possibly underestimated. The associated cancer risk could be similar to that due to a MLH1 sequence variant. MLH1 epimutations could be secondary to other genetic defects and follow an autosomal dominant inheritance. On the contrary, primary epimutations are often “ de novo” events, and their transmission does not follow Mendelian rules.

PURPOSE:Low-dose tamoxifen 5 mg/day (babytam) for 3 years can decrease the incidence of new breast cancer events in women with breast intraepithelial neoplasia by 42% with limited toxicity, which provides a new treatment option for these disorders. However, predictive biomarkers of babytam efficacy are lacking. We studied whether baseline levels of insulin-like growth factor-1 (IGF-I), IGF-binding protein-3 (IGFBP-3), estradiol, and sex hormone-binding globulin (SHBG) and their ratios predict babytam efficacy on breast cancer events in a preplanned secondary analysis. PATIENTS AND METHODS:Within a 1:1 placebo-controlled, multicenter randomized trial of babytam or placebo administered for 3 years after surgery in women with hormone-sensitive or unknown breast intraepithelial neoplasia, including atypical ductal hyperplasia and lobular or ductal carcinoma in situ, 406 of 500 participants consented to blood sampling at baseline and at 1 and 3 years. Serum IGF-I, IGFBP-3, estradiol, and SHBG levels and their ratios were measured using chemiluminescent immunoassays. Biomarker changes were estimated using mixed-effects models, and incidence rate ratios were calculated after 10 years of follow-up with Poisson regression. Subgroup analyses were performed using an interaction test and subpopulation treatment effect pattern plot. RESULTS:Baseline levels of IGFBP-3 in the three top quartiles (≥3.44 µg/mL), but not in the lower quartile, predicted greater babytam efficacy compared with placebo (Pinteraction = 0.006). Baseline IGF-I, estradiol, or SHBG levels were not predictive of babytam efficacy, whereas the IGF-I/IGFBP-3 ratio was borderline significant (Pinteraction = 0.067). CONCLUSIONS:High baseline levels of IGFBP-3 (≥3.44 µg/mL) predicted babytam efficacy and may help differentiate which women benefit most from this treatment.

Abstract Exemestane is an effective drug to reduce breast cancer risk reaching an overall 65% reduction in breast cancer in the placebo–controlled phase III MAP.3 trial. To improve its acceptability in primary prevention programs, we are seeking the minimal effective dose. In a 3-arm presurgical trial of 4-6 weeks before breast surgery in 180 postmenopausal women with ER-positive breast cancer, we investigated the activity of alternative exemestane schedules: 25 mg per day (QD), 25 mg three times/week (TIW) or 25 mg per week (QW) and showed that in adherent participants TIW was not inferior to QD in reducing circulating estradiol (Serrano et al JAMA Oncol. doi:10.1001/jamaoncol.2023.0089). Moreover, Ki67 reduction was seen in all arms with no significant difference among arms. Here, we analyzed the concentration of sex steroids, exemestane, and its main metabolite in the cancer and adjacent non-cancerous breast tissue. Tissues samples were homogenized before liquid-liquid extraction. After reconstitution, samples were analyzed by coupling liquid chromatography with tandem mass spectrometry (Sciex QTRAP 6500, Nexera system, Shimadzu). We obtained breast cancer tissue from 93 and non-cancerous breast tissue from 117 participants to measure exemestane, 17-OH-exemestane, and sex steroids. Exemestane and 17-OH-exemestane concentrations were detectable only in the QD arm, while in TIW and QW arms levels were below the Lower Limit of Detection (< LLD). Median exemestane level was 3807 fmol/g and 17485 fmol/g and median 17-OH-exemestane level was 338 fmol/g and 1343 fmol/g in cancer and non-cancerous tissue, respectively. Interestingly, drug and its metabolite accumulated 4-5-fold in non-cancerous tissue compared to cancer tissue in the QD arm. Despite the between-arm drug concentration difference, estradiol was almost completely suppressed in all arms in the non-cancerous tissue, attaining level < LLD in QD and TIW arms, and barely detectable in QW arm. The median in the QW arm was < LLD (< LLD, interquartile range < LLD, 25.5 fmol/g) showing no differences in QD vs TIW and QD vs QW (p = 0.364 and p = 0.693 respectively). While a dose-response trend was observed in cancer tissue, estradiol level was < LLD (< LLD,52.2 fmol/g) on QD, 17.1 (< LLD, 125.3) on TIW, and 128 (< LLD, 224.8) on QW (p=0.046 QD vs TIW arms). Estrone showed a clear dose response trend among arms, whereas no differences were observed for testosterone and androstenedione for both cancer and non-cancerous tissue in all arms. The Ki-67 change was analyzed in the previous paper; here we report the data for those patients who had drug and hormones tissue concentration measured, where Ki-67 decreased in all arms: median Ki67 change from baseline was QD -8 (-10, -3), TIW -6 (-11, -2), QW -4 (-8, -1). Conclusions: Exemestane 25 mg three times a week maintains comparable activity to the standard dose on tissue estradiol suppression and Ki67 decrease. Considering the estradiol suppression in non-cancerous tissue of the lowest exemestane dose, QW might even be considered for breast cancer risk reduction in primary prevention. Further analyses are ongoing to investigate the correlation with other biomarkers including the role of polymorphic UGT2B17 genotype that could identify candidates to lower exemestane dosage. Citation Format: Davide Serrano, Harriet Johansson, Bjørn-Erik Bertelsen, Gunnar Mellgren, Parijatham Thomas, Katherine Crew, Nagi B Kumar, Debora Macis, Valentina Aristarco, Aliana Guerrieri Gonzaga, Sara Gandini, Mauro D’Amico, Tania Buttiron Webber, Irene Maria Briata, Stefano Spinaci, Viviana Galimberti, Giuseppe Viale, Lana A. Vornik, Eduardo Villar-Sanchez, Powel Brown, Brandy M Heckman-Stoddard, Eva Szabo, Bernardo Bonanni, Andrea De Censi. Exemestane and breast cancer prevention: how low can we go? Drug and biomarker tissue levels in a randomized presurgical trial on exemestane alternative dosing regimen [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS07-01.

Fenretinide, a retinoid with a low-toxicity profile that accumulates in the breast, has been shown to prevent second breast cancer in young women. Fenretinide exhibits apoptotic and antiinvasive properties and it improves insulin sensitivity in overweight premenopausal women with insulin resistance. This study aimed to further characterize its role in cancer prevention by measuring circulating biomarkers related to insulin sensitivity and breast cancer risk.Sixty-two women, ages 20 to 46 years, healthy or who had already undergone breast cancer surgery, with a known BRCA1/2 mutation or a likelihood of mutation ≥20% according to the BRCAPRO model, were randomly assigned to receive fenretinide (200 mg/day) or placebo for 5 years (trial registration: EudraCT No. 2009-010260-41). Fasting blood samples were drawn at baseline, 12 and 36 months, and the following biomarkers were analyzed: retinol, leptin, adiponectin, retinol-binding protein 4 (RBP-4), total cholesterol, high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol, triglycerides, glucose, insulin, insulin-like growth factor (IGF-1), IGF-binding protein 3, sex hormone binding globulin (SHBG), testosterone, and vascular endothelial growth factor (VEGF).After 12 months of treatment, we observed a favorable effect of fenretinide on glucose (decrease; P = 0.005), insulin (decrease; P = 0.03), homeostatic model assessment index (decrease; P = 0.004), HDL cholesterol (increase; P = 0.002), even though these effects were less prominent after 36 months. Retinol and retinol-binding protein 4 markedly decreased (P < 0.0001) throughout the study. None of the other measured biomarkers changed. PREVENTION RELEVANCE:Fenretinide exhibits beneficial effects on the metabolic profile, supporting its clinical use in breast cancer prevention especially in premenopausal women with a positive family history and pathogenic variants in BRCA1/2 genes. This finding requires further investigations in larger trials to confirm its role in breast cancer prevention.

Background Breast Cancer (BC) prevention strategies range from lifestyle changes such as increasing physical activity and reducing body weight to preventive drugs like tamoxifen, known to reduce BC incidence in high-risk women. Sex Hormone Binding Globulin (SHBG) is related to BC risk due to its ability to bind circulating estradiol at high affinity and to regulate estradiol action. A study protocol is presented based on the assessment of the effect of different interventions such as tamoxifen at 10 mg every other day (LDT), intermittent caloric restriction (ICR) two days per week, lifestyle intervention (LI, step counter use) and their combination on the modulation of SHBG and several other biomarkers associated to BC. Methods A randomized phase II biomarker study will be conducted in 4 Italian centers. Unaffected women aged between 18 and 70 years, carriers of a germline pathogenetic variant (BRCA1, BRCA2, PALB2, or other moderate penetrance genes), or with a >5% BC risk at 10 years (according to the Tyrer-Cuzick or the Breast Cancer Surveillance Consortium Risk models) or with a previous diagnosis of intraepithelial neoplasia will be eligible. A total of 200 participants will be randomized to one of the four arms: LDT; LDT + ICR; LI; LI + ICR. Interventions will span six months, with baseline and follow-up clinic visits and interim phone calls. Discussion The aim of the study is to verify whether LDT increases circulating SHBG more than LI with or without ICR after 6 months. Secondary objectives include assessing HOMA-index, inflammatory markers, adiponectin/leptin ratio, quality of life (QoL), safety, toxicity, mammographic density, and changes in microbiome composition across groups. The study’s innovation lies in its inclusion of diverse BC risk categories and combination of pharmaceutical and behavioral interventions, potentially enhancing intervention efficacy while balancing tamoxifen’s side effects on QoL, especially menopausal symptoms. Trial registration EuCT number:2023-503994-39-00; Clinical trials.gov NCT06033092.

In a 3-arm presurgical trial, four-six weeks exemestane 25 mg three times/week (TIW) was non-inferior to 25 mg/day (QD) in suppressing circulating estradiol in postmenopausal women with ER-positive breast cancer. Since obesity may decrease exemestane efficacy, we analyzed changes in sex steroids, adipokines, Ki-67, and drug levels in relation to obesity. Postmenopausal women with early-stage ER-positive breast cancer were randomized to either exemestane 25 mg QD (n = 57), 25 mg TIW (n = 57), or 25 mg/week (QW, n = 62) for 4–6 weeks before breast surgery. Serum and tissue pre- and post-treatment biomarkers were stratified by body mass index (BMI)< or ≥30 kg/m2. Post-treatment median exemestane and 17-OH exemestane levels were 5–6 times higher in the QD arm compared to the TIW arm. For obese women, TIW maintained comparable reductions to QD in systemic estradiol levels, although the reduction in estrone was less with the TIW regimen. There was less suppression of SHBG with the TIW versus the QD dose schedule in obese women which should result in less systemic bioavailable estrogens. Metabolically, the effect of the TIW regimen was similar to the QD regimen for obese women in terms of leptin suppression and increase in the adiponectin-leptin ratio. Reduction in tissue Ki-67 was less for obese women on the TIW regimen than QD, although changes were similar for non-obese women. Our findings suggest that TIW exemestane should be explored further for primary cancer prevention in both normal weight and obese cohorts.

10510 Background: Babytam (BT), 5 mg/day for 3 years (y) is a popular choice for preventive therapy after breast DCIS/LCIS/ADH given its 10-y efficacy to prevent recurrence without adverse events (1). Here we investigated the effect of BT on serum biomarkers and their role as prognostic and predictive factors. Methods: In a phase-III trial of BT or placebo (P), 406 out of 500 women consented to blood sampling at baseline, 1 and 3 y. Serum estradiol (E2), SHBG, IGF-I, IGFBP-3 and their molar ratios were measured by CLIA. Biomarker changes were estimated with mixed-effects models for repeated measures and Incidence Rate Ratios (IRR) of the primary endpoint (invasive breast cancer or DCIS) were calculated after 5 and 10 y of follow-up with Poisson regression. Subgroup analyses were performed by interaction test. Results: There were no differences in event rates between women with blood samples and those w/out. Compared with P at 1 y, IGF-I/IGFBP-3 decreased by 0.039 (95%CI, 0.027-0.052), relative difference (rd), 22% (15-29) (p<0.001), whereas E2/SHBG increased by 2.967 (1.767-4.166), rd, 79% (47-111) in pre- and decreased by 0.121 (-1.117-0.874), rd, -9% (-84-66), in postmenopausal women on BT (p-interaction=0.001). The mean annual rate of events (x1000 PY) after 5 and 10 y follow-up according to baseline level of IGF-I/IGFBP-3 (all women) and E2/SHBG (postmenopausal). Conclusions: BT significantly lowers IGF-I/IGFBP-3 ratio, increases E2/SHBG in premenopause to a lesser extent than 20 mg/d and is effective in most subgroups regardless of baseline biomarker levels. While lower baseline IGF-I/IGFBP-3 levels were predictive of BT efficacy at 5 and 10 y, higher levels at 10 y were associated with a lower benefit of BT. E2/SHBG had a tendency to be prognostic and predictive of BT efficacy at 5 y, but softened down at 10 y. These biomarkers may help differentiate which women benefit most from BT. The role of IGF-I change as surrogate biomarker of BT effect requires further studies. 1. Lazzeroni et al: JCO 41:3116, 2023. Clinical trial information: NCT01357772 . [Table: see text]