Guenther, Joseph M.

Importance Adding fulvestrant to anastrozole (A+F) improved survival in postmenopausal women with advanced estrogen receptor (ER)–positive/ERBB2 (formerly HER2)–negative breast cancer. However, the combination has not been tested in early-stage disease. Objective To determine whether neoadjuvant fulvestrant or A+F increases the rate of pathologic complete response or ypT1-2N0/N1mic/Ki67 2.7% or less residual disease (referred to as endocrine-sensitive disease) over anastrozole alone. Design, Setting, and Participants A phase 3 randomized clinical trial assessing differences in clinical and correlative outcomes between each of the fulvestrant-containing arms and the anastrozole arm. Postmenopausal women with clinical stage II to III, ER-rich (Allred score 6-8 or >66%)/ERBB2-negative breast cancer were included. All analyses were based on data frozen on March 2, 2023. Interventions Patients received anastrozole, fulvestrant, or a combination for 6 months preoperatively. Tumor Ki67 was assessed at week 4 and optionally at week 12, and if greater than 10% at either time point, the patient switched to neoadjuvant chemotherapy or immediate surgery. Main Outcomes and Measures The primary outcome was the endocrine-sensitive disease rate (ESDR). A secondary outcome was the percentage change in Ki67 after 4 weeks of neoadjuvant endocrine therapy (NET) (week 4 Ki67 suppression). Results Between February 2014 and November 2018, 1362 female patients (mean [SD] age, 65.0 [8.2] years) were enrolled. Among the 1298 evaluable patients, ESDRs were 18.7% (95% CI, 15.1%-22.7%), 22.8% (95% CI, 18.9%-27.1%), and 20.5% (95% CI, 16.8%-24.6%) with anastrozole, fulvestrant, and A+F, respectively. Compared to anastrozole, neither fulvestrant-containing regimen significantly improved ESDR or week 4 Ki67 suppression. The rate of week 4 or week 12 Ki67 greater than 10% was 25.1%, 24.2%, and 15.7% with anastrozole, fulvestrant, and A+F, respectively. Pathologic complete response/residual cancer burden class I occurred in 8 of 167 patients and 17 of 167 patients, respectively (15.0%; 95% CI, 9.9%-21.3%), after switching to neoadjuvant chemotherapy due to week 4 or week 12 Ki67 greater than 10%. PAM50 subtyping derived from RNA sequencing of baseline biopsies available for 753 patients (58%) identified 394 luminal A, 304 luminal B, and 55 nonluminal tumors. A+F led to a greater week 4 Ki67 suppression than anastrozole alone in luminal B tumors (median [IQR], −90.4% [−95.2 to −81.9%] vs −76.7% [−89.0 to −55.6%]; P < .001), but not luminal A tumors. Thirty-six nonluminal tumors (65.5%) had a week 4 or week 12 Ki67 greater than 10%. Conclusions and Relevance In this randomized clinical trial, neither fulvestrant nor A+F significantly improved the 6-month ESDR over anastrozole in ER-rich/ERBB2-negative breast cancer. Aromatase inhibition remains the standard-of-care NET. Differential NET response by PAM50 subtype in exploratory analyses warrants further investigation. Trial Registration ClinicalTrials.gov Identifier: NCT01953588

Importance Oral tamoxifen citrate benefits women with ductal carcinoma in situ (DCIS), but concern about toxic effects has limited acceptance. Previous pilot studies have suggested transdermal 4-hydroxytamoxifen gel has equivalent antiproliferative efficacy to oral tamoxifen, with low systemic exposure. Objective To demonstrate that 4-hydroxytamoxifen gel applied to the breast skin is noninferior to oral tamoxifen in its antiproliferative effect in DCIS lesions. Design, Setting, and Participants This randomized, double-blind, phase 2 preoperative window trial was performed at multicenter breast surgery referral practices from May 31, 2017, to January 27, 2021. Among 408 women with estrogen receptor–positive DCIS who were approached, 120 consented and 100 initiated study treatment. The most common reasons for nonparticipation were surgical delay, disinterest in research, and concerns about toxic effects. Data were analyzed from January 26, 2021, to October 5, 2022. Intervention Random assignment to oral tamoxifen citrate, 20 mg/d, and gel placebo or 4-hydroxytamoxifen gel, 2 mg/d per breast, and oral placebo, for 4 to 10 weeks, followed by DCIS resection. Main Outcomes and Measures The primary end point was absolute change in DCIS Ki-67 labeling index (Ki67-LI). Secondary end points included 12-gene DCIS Score, breast tissue tamoxifen metabolite concentrations, tamoxifen-responsive plasma protein levels, and patient-reported symptoms. Noninferiority of Ki67-LI reduction by 4-hydroxytamoxifen gel was tested using analysis of covariance; within- and between-arm comparisons were performed with paired t tests for mean values or the Wilcoxon rank sum test for medians. Results Of 90 participants completing treatment (mean [SD] age, 55 [11] years; 8 [8.9%] Asian, 16 [17.8%] Black, 8 [8.9%] Latina, and 53 [58.9%] White), 15 lacked residual DCIS in the surgical sample, leaving 75 evaluable for the primary end point analysis (40 in the oral tamoxifen group and 35 in the 4-hydroxytamoxifen gel group). Posttreatment Ki67-LI was 3.3% higher (80% CI, 2.1%-4.6%) in the 4-hydroxytamoxifen gel group compared with the oral tamoxifen group, exceeding the noninferiority margin (2.6%). The DCIS Score decreased more with oral tamoxifen treatment (−16 [95% CI, −22 to −9.4]) than with 4-hydroxytamoxifen gel (−1.8 [95% CI, −5.8 to 2.3]). The median 4-hydroxytamoxifen concentrations deep in the breast were nonsignificantly higher in the oral tamoxifen group (5.7 [IQR, 4.0-7.9] vs 3.8 [IQR, 1.3-7.9] ng/g), whereas endoxifen was abundant in the oral tamoxifen group and minimal in the 4-hydroxytamoxifen gel group (median, 13.0 [IQR, 8.9-20.6] vs 0.3 [IQR, 0-0.3] ng/g; P < .001). Oral tamoxifen caused expected adverse changes in plasma protein levels and vasomotor symptoms, with minimal changes in the transdermal group. Conclusions and Relevance In this randomized clinical trial, antiproliferative noninferiority of 4-hydroxytamoxifen gel to oral tamoxifen was not confirmed, potentially owing to endoxifen exposure differences. New transdermal approaches must deliver higher drug quantities and/or include the most potent metabolites. Trial Registration ClinicalTrials.gov Identifier: NCT02993159

Abstract Background: Adjuvant oral tamoxifen (TAM) benefits women with DCIS, but toxicity concerns have limited its acceptance. Transdermal therapy with 4-hydroxy tamoxifen (4-OHT) gel applied to the breast skin is a possible solution. Previous pilot data suggest equivalent anti-proliferative efficacy of TAM and 4-OHT gel, but minimal systemic exposure with transdermal therapy. We report a prospective double blinded randomized phase 2 trial comparing TAM to 4-OHT gel in women with DCIS. Methods: 107 women with estrogen receptor positive (≥10%) DCIS were randomized to TAM (20 mg/day + placebo gel) or 4-OHT gel (2mg 4-OHT gel/breast, bilaterally + oral placebo), for 4-10 weeks prior to surgery. The primary endpoint was reduction in DCIS Ki67 labeling index (LI). Secondary endpoints included the 12-gene DCIS Score assay (Exact Sciences), breast tissue and plasma concentrations of 4-OHT and endoxifen, TAM-responsive circulating proteins, and patient reported symptoms (Breast Eight Symptom Scale). We estimated that 80 evaluable participants would provide 80.5% power to establish non-inferiority of 4-OHT, defined as relative Ki67-LI decline >35% and absolute decline >2.6%, with one-sided 𝛼=0.10. Non-inferiority of 4-OHT gel for Ki67-LI reduction was tested using an ANCOVA model. Statistical comparisons within- and between-arms were calculated with paired t-test and Welch Two Sample t-test, respectively. Results: 72 of 87 women adhered to the protocol, and were evaluable for the primary endpoint (39 TAM and 33 4-OHT gel). Mean treatment duration was 47 days for TAM and 44 days for 4-OHT gel (p=0.2). The median absolute decline in Ki67 labeling index was significant in the oral TAM (-3.7%, p< 0.001) but not in 4-OHT gel arm (-1.3%, p=0.2) (p=0.002). Ki67 results following menopausal stratification also favored the TAM arm: (-1.3%; p=0.06 in 37 premenopausal women and -3.7%; p=0.02 in 35 postmenopausal women). Similarly, DCIS score showed a significantly greater reduction in the TAM (-14, p< 0.001) but not in the 4-OHT gel arm (-4, p=0.1). Tissue 4-OHT concentrations were non-significantly higher in the TAM arm and were similar between superficial and deep sampling locations (superficial 6.1 and 4.2 ng/g for TAM and 4-OHT gel, respectively, p= 0.55; deep 5.7 and 3.8 ng/g, respectively, p= 0.06), whereas plasma 4-OHT concentration was markedly lower in the gel group (2 ng/mL and 0.24 ng/mL for TAM and 4-OHT gel, respectively, P < 0.001). Endoxifen was abundant in plasma (11 ng/mL) and deep tissue (13 ng/g) of the TAM arm, but present in trace amounts in the 4-OHT gel arm (undetectable in plasma and 0.31 ng/g in tissue; p < 0.001). Circulating TAM responsive markers (insulin like growth factor 1, sex hormone binding globulin, von Willebrand factor, and protein S total) and vasomotor symptoms were significantly and unfavorably modulated by TAM, but not by 4-OHT gel therapy. Conclusions: The non-inferiority of transdermal 4-OHT gel to Tam in terms of anti-proliferative effect in DCIS lesions was not demonstrated at the doses used for this study. DCIS Score analysis gave similar results. Tissue 4-OHT concentration in 4-OHT gel and Tam-treated subjects was roughly similar. However, endoxifen exposure was higher with oral TAM therapy and may partially explain the observed differences in major endpoints. In future studies, use of higher 4-OHT gel doses, longer duration of treatment, or different formulation may overcome these. Citation Format: Oukseub Lee, Xinlei Mi, Yanfei Xu, Luis Blanco, Azza M. Akasha, Kelly Benante, Shanshan Zhang, Carissa LaBoy, Thomas Helland, Melissa Pilewskie, Amy Degnim, Zahraa Al-Hilli, Amanda L. Amin, E Shelley Hwang, Joseph M. Guenther, Simon Steinar Hustad, Demirkan B. Gursel, Masha Kocherginsky, Gunnar Mellgren, Eileen Dimond, Marjorie Perloff, Brandy M. Heckman-Stoddard, Seema Khan. PD15-12 A pre-surgical window trial of oral tamoxifen versus transdermal 4-hydroxytamoxifen gel in women with estrogen receptor positive duct carcinoma in situ (DCIS) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD15-12.

Abstract Introduction: The ALTERNATE trial randomized postmenopausal women with ER Allred 6-8 HER2- breast cancer to 6 months of NET with anastrozole (A), fulvestrant (F) or the combination (A+F). Biopsies were taken preNET and after 4-weeks(wks). Patients with Ki67 values >10% at 4-wks were offered triage to neoadjuvant chemotherapy. Patients with on-treatment Ki67 ≤ 10% who completed NET underwent surgery and Ki67 was reassessed. The primary endpoint was endocrine-sensitive disease rate (ESDR). ESD is defined as pCR or PEPI-0 residual disease (pT1-2, pN0, Ki67 ≤ 2.7%). We previously reported that the ESDR difference between the F-containing arms and the A arm was not >10% (ASCO 2020) and that baseline RNA-seq-based intrinsic subtypes predicted outcomes overall (SABCS 2021). Herein we describe relationships between PAM50 intrinsic subtype and Ki67 values by treatment arm because comparative drug effectiveness in adjuvant endocrine therapy studies in ER+ HER2- breast cancer can be predicted by the degree of Ki67 suppression (PMC3518447). Methods: 743 of the 1297 eligible patients (A: 264; F: 231; A+F: 248) had RNA extracted from preNET frozen tumor biopsies with >50% tumor content and subjected to RNA seq. Intrinsic subtypes were then assigned as LumA, LumB, and NonLum (Basal or HER2-E) using open-source PAM50-based informatics. Differences in the proportion with wk4 Ki67 > 10%, % change in wk4 ki67, and surgical CCCA (Ki67 ≤ 2.7%) rate (sxCCCA) between treatments and by intrinsic subtype was assessed using stratified logistic regression, Wilcoxon rank sum test, and Fisher’s exact test, respectively. Analysis of sxCCCA excluded those who failed to complete NET for reasons other than disease progression or early Ki67 >10%. Results: Amongst the 358 LumA cases there were no significant differences in Ki67-based endpoints between treatments. Among the 292 LumB cases, the wk4 ki67 > 10% rate was lower with A+F (19.4%) than A (43%) (P=0.0002) and was somewhat lower in F (31%) versus A (P=0.076). The % change in wk4 Ki67 in LumB cases, adjusted for baseline Ki67, showed markedly superior suppression for A+F versus A (-90% vs. -77%; P=<0.0001) and versus F (-90% vs. -80%; P=0.0026). Furthermore sxCCCA rates were significantly higher with A+F than A (53% vs. 25% P = <0.0001) and somewhat higher for F (37%) than A (p=0.068), indicating that superior antiproliferative effects for A+F persist after 6 months on therapy. Lack of Ki67 suppression in response to treatment was observed in the majority of 43 NonLum samples regardless of treatment. Conclusion: The combination of A+F was significantly more effective than either drug alone for the control of LumB breast cancer cell proliferation. This suggests that A+F may be a more effective adjuvant endocrine therapy than A alone in LumB disease. The lower Ki67 suppression with A alone also suggests that poorer outcome in some LumB tumors may be due to insufficient ER targeting rather than ER-independent tumor growth Support: U10CA180821, U10CA180882, U24CA196171, UG1CA189856, U10CA180868 (NRG), NCI BIQSFP, BCRF, Genentech, AstraZeneca. https://acknowledgments.alliancefound.org. (MJE) CPRIT RR140033, P50-CA186784, P50-CA58223, U01-CA214125, U24-CA210954, Gift from Ralph and Lisa Eads, McNair Scholarship. ClinicalTrials.gov Identifier: NCT01953588 Citation Format: Matthew J. Ellis, Meenakshi Anurag, Jeremy Hoog, Aranzazu Fernandez-Martinez, Cheng Fan, Richard Gibbs, Souzan Sanati, Kiran Vij, Mark Watson, Travis Dockter, Olwen Hahn, Joseph Guenther, Abigail Caudle, Erica Crouch, Amy Tiersten, Monica Mita, Wajeeha Razaq, Tina J. Hieken, Yang Wang, A. Marilyn Leitch, Gary W. Unzeitig, Eric Winer, Anna Weiss, Kelly Hunt, Ann H. Partridge, Charles M. Perou, Vera Suman, Cynthia X. Ma, Lisa A. Carey. The effect of intrinsic subtype on inhibition of tumor growth by anastrozole vs. fulvestrant vs. the combination: Results from the Alliance neoadjuvant endocrine therapy (NET) ALTERNATE trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT026.

Abstract Background: Neoadjuvant ET (NET) offers an opportunity to assess ET sensitivity for ER+ HER2- BC and potentially to tailor therapy. Ki67 >10% on biopsy after 2-4 weeks (wks) of NET identifies patients (pts) with intrinsic ET resistance; while pathologic complete response (pCR) and modified preoperative endocrine prognostic index of 0 (mPEPI 0: pT1-2N0, Ki67 ≤2.7%) at surgery indicates sensitivity to ET. However, on-NET biopsy is not always acceptable or feasible and delays the ET sensitivity determination. PAM50 ROR score and intrinsic subtypes by tumor RNA profiling are prognostic in pts with early stage ER+ HER2- BC, and predict pCR rates to neoadjuvant chemotherapy (NCT) (PMC2667820). We therefore hypothesized that PAM50 analysis on pre-NET biopsies could predict the likelihood of a) a high on-NET Ki67, b) mPEPI-0 or pCR at surgery and, c) pCR for pts triaged to NCT. Methods: The ALTERNATE trial is a phase III study that randomized postmenopausal pts with clinical stage II/III ER+ (Allred score 6-8) HER2- BC to receive neoadjuvant anastrozole, fulvestrant, or both for 6 months before surgery. Research biopsy was required at pre-NET and wk 4, then optional at wk 12. Pts with Ki67 >10% on biopsy at wk 4 or 12 discontinued NET and were offered NCT. PAM50 intrinsic subtype and ROR-P values were generated from mRNA sequencing (RNASeq) analysis on pre-NET biopsies using open-source informatics (PMC7723687) and evaluated for prediction of on-NET Ki67 >10% at wk 4 or 12, pCR or mPEPI-0 post NET, and pCR post NCT. Results: 749 of 1,297 eligible trial pts were included in the analyses, after excluding 548 pts due to insufficient pre-NET tumor for RNASeq (n=511) or PAM50 normal subtype (n=37). Similar to the entire ALTERNATE population, the rate of Ki67 >10% at wk 4 or 12 was 24.4% (95% CI: 21.4-27.7%) and the rate of mPEPI-0/pCR post NET was 19.8% (95% CI: 17.0-22.8%). There were 393 (52.5%) Lum A, 302 (40.3%) Lum B, and 54 (7.2%) non-Lum (9 Basal, 45 HER2-E) BCs. These included 196 (26.2%) ROR-P low, 354 (47.3%) ROR-P medium and 199 (26.6%) ROR-P high BCs. Both the rates of Ki67 >10% at wk 4 or 12 and mPEPI-0/pCR differed significantly with respect to PAM50 subtype or ROR-P category, such that Lum A or ROR-P low BCs were least likely to have a Ki67 >10% at wk 4 or 12 and most likely to achieve mPEPI-0/pCR (Table). 93 of 168 (55.4%) pts triaged to NCT had RNA-seq results, yielding 26 Lum A, 49 Lum B, 4 Basal and 14 HER2-E, with the pCR rates of 0%, 6.1%, 0%, and 21.4%, respectively. There were 10 ROR-P low, 39 medium, and 44 high tumors, with a pCR rate of 0%, 5.1% and 9.1%, respectively. Conclusion: These data indicate that both baseline ROR-P and intrinsic subtype are predictive of early on-NET Ki67 > 10% and mPEPI 0/pCR at surgery after NET. For pts triaged to NCT based on an early on-NET Ki67 >10%, the HER2-E group had the highest pCR rate (20%) and no pCRs were observed in Lum A. These data may be useful for directing neoadjuvant therapy in postmenopausal pts with ER+ HER2- BC. Support: U10CA180821, U10CA180882, U24CA196171, UG1CA189856, U10CA180868 (NRG), NCI BIQSFP, BCRF, Genentech, AstraZeneca. https://acknowledgments.alliancefound.org. (MJE) CPRIT RR140033, P50CA186784, P50-CA58223, U01 CA214125, U24CA210954, Gift from Ralph and Lisa Eads, McNair Scholarship. Trials.gov Identifier: NCT01953588. Table 1.Rates of Ki67 >10% and mPEPI-0/pCR post NET by PAM50 subtype and ROR-P categoryKi67 >10% at wk 4 or 12mPEPI 0/pCR post NETPAM50 SubtypenYes, n (%)PnNo, n (%)PLum A37251 (13.7%) 95% CI: 10.4-17.6%<0.0001393104 (26.5%) 95%CI: 22.2-31.1%<0.0001Lum B29394 (32.1%) 95% CI: 26.8-37.8%30243 (14.2%) 95%CI: 10.5-18.7%Non-luminal (Basal and HER2-E)5338 (71.7%) 95%CI: 57.6-83.2%541 (1.9%) 95%CI: 0.05-9.9%ROR-P CategorynYes, n (%)PnNo, n (%)PLow18018 (10.0%) 95%CI: 6.0-15.3%<0.000119660 (30.6%) 95%CI: 24.2-37.6%<0.0001Intermediate34474 (21.5%) 95%CI: 17.3-26.2%35471 (20.1%) 95%CI: 16.0-24.6%High19491 (46.9%) 95%CI: 39.7-54.2%19917 (8.5%) 95%CI: 5.1-13.3% Citation Format: Cynthia X Ma, Meenakshi Anurag, Travis Dockter, Jeremy Hoog, Aranzazu Fernandez-Martinez, Cheng Fan, Richard Gibbs, Souzan Sanati, Kiran Vij, Mark Watson, Olwen Hahn, Joseph Guenther, Abigail Caudle, Erika Crouch, Amy Tiersten, Monica Mita, Wajeeha Razaq, Tina J Hieken, Yang Wang, A. Marilyn Leitch, Gary W Unzeitig, Anna Weiss, Eric P Winer, Kelly Hunt, Ann H Partridge, Lisa A Carey, Charles M Perou, Matthew J Ellis, Vera Suman. Pam50 intrinsic subtype and risk of recurrence score (ROR) for the prediction of endocrine (ET) sensitivity and pathologic response to chemotherapy in postmenopausal women with clinical stage II/III estrogen receptor positive (ER+) and HER2 negative (HER2-) breast cancer (BC) in the alternate trial (Alliance A011106) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD9-03.

Abstract Background: NET is offered to postmenopausal patients (pts) with clinical stage 2/3 ER+/HER2- BC to promote breast-conserving surgery. Also limited surgical accessibility during the COVID19 pandemic has increased NET utility. Inability to identify ET-resistant disease at diagnosis risks disease progression (PD) and delays more effective treatments. Dowsett et al. recently demonstrated that baseline levels of ER, progesterone receptor (PR), Ki67 (>15% vs ≤15%), and Ki67 (>10% vs ≤10%) 2-4 weeks (wks) after starting NET may improve appropriate patient (pt) selection for NET (PMC7280290). The ER, PR and Ki67-based prediction model divides pts with primary ER+/HER2- BC into 3 groups for appropriateness for NET: (Group 1) NET is likely to be inappropriate (Allred ER <6 or ER 6 and PgR <6), (Group 2) NET may be appropriate and a biopsy for on-treatment Ki67 analysis may be considered after 2-4 wks of NET (2A: ER 7 or 8 and PgR <6 and 2B: ER 6 or 7 and PgR ≥6) given that on-treatment Ki67 >10% has been associated with worse outcome (PMC5455353), or (Group 3) NET is appropriate (ER 8 and PgR ≥6). The ALTERNATE trial (NCT01953588) randomized postmenopausal women with clinical stage II or III, ER+ (Allred score 6-8)/HER2- BC to receive anastrozole (ANA), fulvestrant (FUL), or ANA + FUL for 6 months, unless Ki67 was >10% on wk 4 or 12 biopsy, in which case pts were triaged to receive neoadjuvant chemotherapy (NCT) or surgery. As previously reported, the ET-sensitive disease (mPEPI 0 plus pCR) rates were similar across the treatment arms and overall 22% (286 of 1,299) pts had Ki67 >10% at wk 4 or 12. The ALTERNATE trial therefore provides a large independent data set to evaluate the NET appropriateness model. Results: Among 1,299 eligible pts randomized to receive 6 months of NET, 214 were excluded due to absent HR Allred score (n=41) or absence of pre-treatment and wk 4 Ki67 determinations (n=173). The proportions of the remaining 1,085 pts in Group 1, 2 and 3 were 1% (n=10), 43% (n= 468), and 56% (n=607), respectively. On-study Ki67 >10% prompting conversion from NET to NCT/Surgery occurred in: Group 1 90% (9 of 10), Group 2 30% (141 of 468), and Group 3 17% (104 of 607) (Table 1). Among the 1,075 pts in Groups 2 and 3, 260 (24%) pts had Ki67 ≤15% at baseline (BL), among whom only 14 (5.4%) had Ki67 >10% at wk 4, compared to 231 of the 815 (28.3%) who had BL Ki67 >15% and subsequent Ki67 >10% at wk 4. 2% of pts who remained on NET due to on-treatment Ki67 <10% had PD. Response and PEPI-0 rates by group will be reported. Conclusion: ALTERNATE trial data support a model whereby levels of ER, PR and Ki67 at diagnosis can be used for the identification of postmenopausal pts with primary ER+/HER2- BC who are appropriate for NET. When baseline ER Allred scores are >6 and Ki67 ≤15%, there is a low likelihood of ET-resistant disease. When BL Ki67 is >15%, ET sensitivity is variable, and on-treatment biopsy for Ki67 may assist in triaging regarding NET appropriateness, particularly given the extremely low local PD rates seen in ALTERNATE when on-treatment Ki67 was <10%. Support: U10CA180821, U10CA180882, U24CA196171, UG1CA189856, U10CA180868 (NRG); NCI BIQSFP, BCRF, Genentech, AstraZeneca. https://acknowledgments.alliancefound.org; Clinical Trials.gov Identifier: NCT01953588 Table 1 Baseline levels of ER, PR, and Ki67 in Relation to Wk 4 Ki67 (N=1,085)BaselineWeek 4GroupNERAllred ScorePRAllred ScoreKi67Ki67 ≤10%N (%)Ki67 >10%N (%)1N=26<6≤15%0 (0%)2 (100%)9 (90)N=86<6>15%1 (12.5%)7 (87.5%)2AN=647 or 8<6≤15%61 (95.3%)3 (4.7%)90 (30.1)N=2357 or 8<6>15%148 (63%)87 (37%)2BN=466 or 7≥6≤15%42 (91.3%)4 (8.7%)51 (30.2)N=1236 or 7≥6>15%76 (61.8%)47 (38.2%)3N=1508≥6≤15%143 (95.3%)7 (4.7%)104 (17.1)N=4578≥6>15%360 (78.8%)97 (21.2%) Citation Format: Matthew J Ellis, Vera Suman, A. Marilyn Leitch, Souzan Sanati, Kiran Vij, Gary W Unzeitig, Jeremy Hoog, Mark Watson, Olwen Hahn, Joseph Guenther, Abigail Caudle, Erika Crouch, Horacio Maluf, Mitch Dowsett, Amy Tiersten, Monica Mita, Wajeeha Razaq, Tina J Hieken, Yang Wang, Travis Dockter, Jo Anne Zujewski, Anna Weiss, Clifford Hudis, Eric P Winer, Kelly Hunt, Ann H Partridge, Cynthia X Ma, Lisa A Carey. Validation of a predictive model for potential response to neoadjuvant endocrine therapy (NET) in postmenopausal women with clinical stage II or III estrogen receptor positive (ER+) and HER2 negative (HER2-) breast cancer (BC): An ALTERNATE trial analysis (Alliance A011106) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD2-10.

Abstract Background: Ki67 values >10% 2-4 weeks (wks) after starting neoadjuvant ET (NET) indicates persistent cell proliferation, resistance to ET, and is associated with increased risk of recurrence. The ACOSOG Z1031 trial suggested that these tumors are also relatively chemotherapy (chemo) resistant with a low pathologic complete response (pCR) rate to NCT. The ALTERNATE trial (NCT01953588) is a randomized study of neoadjuvant anastrozole (ANA), fulvestrant (FUL), or ANA + FUL in postmenopausal patients (pt) with newly diagnosed clinical stage II or III ER+ (Allred score 6-8)/HER2- BC. Ki67 >10% at wk 4 or 12 after starting NET triggered triage to NCT of physician choice or weekly paclitaxel. Pts who refused protocol-directed therapy, were not candidates for NCT, or decided to undergo immediate surgery are being followed per protocol. Here we report the rates of pCR and residual cancer burden (RCB) following NCT for pts triaged to NCT due to Ki67 >10% at wk 4 or 12. Results: Of the 1,299 eligible pts randomized to receive ANA, FUL, or ANA + FUL, 286 (22%) had Ki67 >10% at wk 4 or 12. 168 of these 286 pts (58.7%) chose to switch to NCT, 32 went to surgery (11.2%), and 86 discontinued further protocol-directed therapy (30.1%). Among the 168 pts who underwent NCT, the presenting clinical T stages were cT2 (n=113; 67.26%), cT3 (n=47; 27.98%) and cT4 (n=8; 4.76%) and N stages were cN0 (n=82; 48.8%), cN1 (n=75; 44.6%), cN2/3 (n=9; 5.4%) and cNx (n=2; 1.2%). Central ER testing was performed on pre-treatment biopsies and confirmed ER Allred score 6-8 in 155 of 168 (92.2%) pts, with the rest being ER Allred score 4-5 (n=5; 3%), ER- (Allred score 0) (n=2; 1.2%), or not tested (n=6; 3.6%). Most (n=139; 82.7%) were ER+/PR+, while 17.3% (n=29) were ER+/PR-, and tumor grades were G1 (n=10; 6%), G2 (n=99; 58.9%), G3 (n=54; 32.1%), not reported (n=5; 3%). Baseline Ki67 levels prior to NET were >10% in 94% (n=158), ≤10% in 3% (n=5), and not done in 3% (n=5). NCT regimens administered included doxorubicin/cyclophosphamide (AC) followed by paclitaxel (T) (n=60; 35.71%); weekly paclitaxel (n=56; 33.33%), docetaxel/cyclophosphamide (TC) (n=33; 19.65%), other doxorubicin and/or taxane containing regimen (n=17; 10.12%), and cyclophosphamide/methotrexate/fluorouracil (CMF) (n=2; 1.19%). 35 (20.8%) pts did not complete planned course of NCT due to toxicity (n=27) or refusal (n=8). 154 NCT pts underwent surgery (mastectomy in 40.3%, and breast conserving surgery in 59.7%). The path ypT stages were Tis/0 (n=10; 6.5%), T1 (n=62; 40.3%), T2 (n=61; 39.6%), and T3/4 (n=21; 13.6%), and the ypN stages were N0 (n=66; 42.9%), N1 (n=57; 37%), N2/3 (n=30; 19.5%), and Nx (n=1; 0.6%). Among the 168 pts who started on NCT (intent to treat population), there were 8 pCRs (no invasive disease in the breast or lymph nodes) (4.8%; 95% CI: 2.1% to 9.2%). Residual Cancer Burden (RCB) categories include RCB 0 (n=8; 4.8%), RCB 1 (n=15; 8.9%), RCB 2 (n=82; 48.8%), RCB 3 (n=42; 25.0%), and not determined (n=21; 12.5%). Correlations of baseline pt and tumor characteristics with pathology response to NCT will also be presented. Conclusion: In pts with NET-resistant ER+/HER2- BC, salvage NCT is not likely to induce a complete or near complete response. More effective treatments are needed for this high-risk ER+/HER2- pt population. Support: U10CA180821, U10CA180882, U24CA196171, UG1CA189856, U10CA180868 (NRG); NCI BIQSFP, BCRF, Genentech, AstraZeneca. https://acknowledgments.alliancefound.org. Clinical Trials.gov Identifier: NCT01953588 Citation Format: Cynthia X Ma, Vera Suman, A. Marilyn Leitch, Souzan Sanati, Kiran Vij, Gary W Unzeitig, Jeremy Hoog, Mark Watson, Olwen Hahn, Joseph Guenther, Abigail Caudle, Erika Crouch, Horacio Maluf, Amy Tiersten, Monica Mita, Wajeeha Razaq, Tina J Hieken, Yang Wang, Travis Dockter, Jo Anne Zujewski, Anna Weiss, Kelly Hunt, Clifford Hudis, Eric P Winer, Matthew J Ellis, Lisa A Carey, Ann H Partridge. Neoadjuvant chemotherapy (NCT) response in postmenopausal women with clinical stage II or III estrogen receptor positive (ER+) and HER2 negative (HER2-) breast cancer (BC) resistant to endocrine therapy (ET) in the ALTERNATE trial (Alliance A011106) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr GS4-05.

PURPOSE Primary endocrine therapy for ductal carcinoma in situ (DCIS) as a potential alternative to surgery has been understudied. This trial explored the feasibility of a short-term course of letrozole and sought to determine whether treatment results in measurable radiographic and biologic changes in estrogen receptor (ER)–positive DCIS. PATIENTS AND METHODS A phase II single-arm multicenter cooperative-group trial was conducted in postmenopausal patients diagnosed with ER-positive DCIS without invasion. Patients were treated with letrozole 2.5 mg per day for 6 months before surgery. Breast magnetic resonance imaging (MRI) was obtained at baseline, 3 months, and 6 months. The primary end point was change in 6-month MRI enhancement volume compared with baseline. RESULTS Overall, 79 patients were enrolled and 70 completed 6 months of letrozole. Of these, 67 patients had MRI data available for each timepoint. Baseline MRI volumes ranged from 0.004 to 26.3 cm 3 . Median reductions from baseline MRI volume (1.4 cm 3 ) were 0.6 cm 3 (61.0%) at 3 months ( P < .001) and 0.8 cm 3 (71.7%) at 6 months ( P < .001). Consistent reductions were seen in median baseline ER H-score (228; median reduction, 15.0; P = .005), progesterone receptor H-score (15; median reduction, 85.0; P < .001), and Ki67 score (12%; median reduction, 6.3%; P = .007). Of the 59 patients who underwent surgery per study protocol, persistent DCIS remained in 50 patients (85%), invasive cancer was detected in six patients (10%), and no residual DCIS or invasive cancer was seen in nine patients (15%). CONCLUSIONS In a cohort of postmenopausal women with ER-positive DCIS, preoperative letrozole resulted in significant imaging and biomarker changes. These findings support future trials of extended endocrine therapy as primary nonoperative treatment of some DCIS.

Purpose Preoperative aromatase inhibitor (AI) treatment promotes breast-conserving surgery (BCS) for estrogen receptor (ER) –positive breast cancer. To study this treatment option, responses to three AIs were compared in a randomized phase II neoadjuvant trial designed to select agents for phase III investigations. Patients and Methods Three hundred seventy-seven postmenopausal women with clinical stage II to III ER-positive (Allred score 6-8) breast cancer were randomly assigned to receive neoadjuvant exemestane, letrozole, or anastrozole. The primary end point was clinical response. Secondary end points included BCS, Ki67 proliferation marker changes, the Preoperative Endocrine Prognostic Index (PEPI), and PAM50-based intrinsic subtype analysis. Results On the basis of clinical response rates, letrozole and anastrozole were selected for further investigation; however, no other differences in surgical outcome, PEPI score, or Ki67 suppression were detected. The BCS rate for mastectomy-only patients at presentation was 51%. PAM50 analysis identified AI-unresponsive nonluminal subtypes (human epidermal growth factor receptor 2 enriched or basal-like) in 3.3% of patients. Clinical response and surgical outcomes were similar in luminal A (LumA) versus luminal B tumors; however, a PEPI of 0 (best prognostic group) was highest in the LumA subset (27.1% v 10.7%; P = .004). Conclusion Neoadjuvant AI treatment markedly improved surgical outcomes. Ki67 and PEPI data demonstrated that the three agents tested are biologically equivalent and therefore likely to have similar adjuvant activities. LumA tumors were more likely to have favorable biomarker characteristics after treatment; however, occasional paradoxical increases in Ki67 (12% of tumors with > 5% increase after therapy) suggest treatment-resistant cells, present in some LumA tumors, can be detected by post-treatment profiling.