Background: Palbociclib is approved for treatment of ER+, HER2- ABC at a standard dose of 125 mg po daily 3 weeks on/1 week off (STD). We evaluated the efficacy, safety, quality of life (QOL) and compliance of a 100 mg continuous daily dose (CDD) of palbociclib based on modeling data that suggested efficacy and tolerability. Methods: Canadian Cancer Trials Group (CCTG) led a randomized phase II trial (CCTG MA38) to estimate the efficacy of palbociclib 100 mg po on CDD schedule (Arm 1) relative to 125 mg po STD schedule (Arm 2) with physician choice endocrine therapy. Eligible patients had ER+, HER2- ABC, post progression on first line metastatic endocrine therapy or progressed while on/within 12 months of completion of adjuvant endocrine therapy. One line of palliative chemotherapy in ABC was allowed. Stratification factors were: visceral metastases, duration of prior endocrine therapy and planned endocrine therapy. Primary Outcome measure was investigator reported PFS; secondary outcome measures included: RR, OS, safety (CTCAE V4.0), and QOL (EORTC QLQ-C30). The sample size was 180 to enable estimation of the HR between arms with the upper bound of the 90% CI 1.36 times the estimated HR and the lower bound is 0.74 times the estimated HR. Results: 180 patients were enrolled across Canada from Dec 2015 to Feb 2017. The database was locked April 16 2018 after prespecified PFS events reached at a median follow-up of 19 months for all patients. For the whole population: median age was 60.5 years (21% ≥ 70 years); ECOG 0/1 95%; postmenopausal 91%; visceral metastases 67%. Planned endocrine therapy: aromatase inhibitor 33%, fulvestrant 57%, tamoxifen 10%. Efficacy analyses CDD vs STD: PFS stratified univariate HR 0.93 (90% CI 0.66-1.30); multivariate Cox model analysis (covariates ECOG PS, age, histology, grade): HR 0.92 (90% CI 0.67-1.25). Median PFS CDD: 9.33 months (90% CI 6.93-13.90) and STD: 11.30 months (90% CI 8.08- 13.83) Secondary analyses CDD vs STD: OS stratified univariate HR: 1.07 (90% CI 0.67-1.69); multivariate HR 1.14 (90%CI 0.75-1.75); median OS for CDD: 20.73 months (90% CI 19.29-23.30) and 21.39 months (90% CI 19.65 to 26.68) for STD. RR and median duration of response: 11.1% vs 12.4% (p=0.84) and 126 vs 169 days (p=0.86), respectively. Palbociclib drug exposure CDD vs STD: median daily dose (mg) 87 vs 125; median dose intensity (mg/week) 571.2 vs 613.5; ≥ 90% planned dose intensity, 41% vs 54%. Dose modification (withhold and/or reduction) rate CDD vs STD for neutropenia was 70% vs 40%. Grade 3/4 neutropenia 69% vs 53%; febrile neutropenia 3% each arm. Non-hematological toxicity profiles were comparable for both arms. No significant differences were seen in QOL domains. Conclusion: Palbociclib is active and tolerable when administered on either a 100 mg CDD or a 125 mg STD schedule. CDD schedule had higher rates of grade 3/4 neutropenia and dose modifications. Post approval evaluation of alternate dosing schedules for targeted therapies provides useful information regarding drug activity, toxicity and adherence. Citation Format: Parulekar WR, Joy AA, Gelmon K, Mates M, Desbiens C, Clemons M, Taylor S, Lemieux J, Bartlett J, Whelan T, Ayoub J-P, Cescon D, Bordeleau L, Rahim Y, Winch C, Chen BE. Randomized phase II study comparing two different schedules of palbociclib plus second line endocrine therapy in women with estrogen receptor positive, HER2 negative advanced/metastatic breast cancer: CCTG MA38 (NCT02630693) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD1-10.

Background: At least 40% of breast cancers are diagnosed in women ≥65 y old and most are hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-). Palbociclib (PAL) is an oral, small-molecule inhibitor of cyclin-dependent kinases 4 and 6. Randomized studies of PAL combined with endocrine therapy (ET) demonstrated significantly improved progression-free survival (PFS) in patients (pts) with treatment-naive and previously treated advanced breast cancer (ABC). Methods: We evaluated the efficacy of PAL+ET vs ET alone in pts aged ≥65-74 and ≥75 y across multiple pivotal randomized phase 2 and 3 studies. Safety and pharmacokinetics (PK) data (blood samples collected from pts in phase 1/2 [PALOMA-1] and phase 1 studies [NCT00141297 and NCT00420056]) for PAL+ET were pooled and compared across age groups. Pts who had not received treatment for ABC were randomized to receive PAL+letrozole (LET) or LET alone/with placebo (PBO; PALOMA-1, open-label/PALOMA-2, double-blind). Pts who had progressed on prior ET were randomized to receive PAL+fulvestrant (FUL) or PBO+FUL (PALOMA-3, double-blind). The primary endpoint for these studies was investigator-assessed PFS. Safety assessments and blood counts occurred at baseline and every 2 weeks for the first 2 cycles and on day 1 of subsequent cycles. Results: Among 872 pts treated with PAL+ET, 221 (25%) were aged ≥65-74 y and 83 (10%) were ≥75 y (PAL+LET: n=528, 162 and 56, respectively; PAL+FUL: n=347, 59 and 27). Median (range) treatment durations were 440 (1-1615) d, 502 (1-1615) d, and 459 (21-1404) d, respectively. Improvement in efficacy endpoints was seen with PAL+ET vs ET across all age groups (Table 1). Incidence of adverse events (AEs), serious AEs and discontinuations due to AEs were similar in the overall population (99%, 19%, 3%) and in pts aged ≥65-74 (99%, 25%, 5%) and ≥75 y (100%, 30%, 6%). Incidence of all grades and grade 3/4 neutropenia were also similar across age groups (overall: 67% and 54%; ≥65-74 y: 64% and 51%; ≥75 y: 77% and 60%). PK analysis showed no clinically relevant differences between arithmetic means, medians, and geometric means of the apparent oral clearance across age groups. Conclusions: PAL in combination with ET is an effective and well-tolerated treatment option for elderly pts with HR+/HER2- endocrine-sensitive and -resistant ABC. A dose adjustment based on age is not required. Sponsor: Pfizer Table 1. PFS in pts ?65-74 and ?75 y (ITT populations)OverallAged ≥65-74 yAged ≥75 yPALOMA-1/PALOMA-2PAL+LET vs528 vs 303162 vs 9456 vs 26LET/LET+PBO,* nHR (95% CI);0.53 (0.44-0.64);0.66 (0.45-0.97);0.31 (0.16-0.61);1-sided P value<0.00010.01620.0002Median PFS (95% CI), mo24.4 (22.0-26.2) vs27.5 (24.2-NR) vsNR (19.2-NR) vs13.6 (11.1-16.4)21.8 (16.3-31.3)10.9 (4.9-24.9)PALOMA-3PAL+FUL vs347 vs 17459 vs 3727 vs 6FUL+PBO, nHR (95% CI);0.46 (0.36-0.59);0.25 (0.14-0.45);0.87 (0.27-2.79);1-sided P value<0.0001<0.00010.4074Median PFS (95% CI), mo9.5 (9.2-11.0) vs16.1 (12.0-NR) vs13.6 (7.5-NR) vs4.6 (3.5-5.6)3.7 (1.9-5.3)7.4 (1.9-NR)HR=hazard ratio; ITT=intent to treat; NR=not reached. *Does not include 5 pts from phase 1 of PALOMA-1. Citation Format: Rugo HS, Turner NC, Finn RS, Joy AA, Verma S, Harbeck N, Moulder S, Masuda N, Im Y-H, Zhang K, Kim S, Sun W, Schnell P, Huang-Bartlett C, Slamon D. Palbociclib in combination with endocrine therapy in treatment-naive and previously treated elderly women with HR+, HER2– advanced breast cancer: a pooled analysis from randomized phase 2 and 3 studies [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-22-03.

Background: For patients with metastatic hormone receptor (HR)-positive, HER2-negative breast cancer who progress on a non-steroidal aromatase inhibitor (NSAI), exemestane plus everolimus (EE) has been shown to prolong progression-free survival in comparison to exemestane alone. In the current era, many patients are now receiving a CDK4/6 inhibitor with first-line NSAI therapy. There is limited data describing the utilization and effectiveness of treatments following hormonal therapy - CDK4/6 inhibitor combinations, including EE. The aim of this study was to describe the real-world clinical experience and outcomes associated with EE amongst patients with and without prior CDK4/6 inhibitor exposure treated in our provincial jurisdiction. Methods: All patients prescribed EE from January 1, 2016 through May 10, 2018 were obtained from the Alberta Health Services CancerControl Breast Data Mart (BDM). Patients with HER2+ disease, had received <1 cycle of EE or who had been on a placebo controlled trial of hormonal therapy +/- CDK4/6 inhibitor prior to EE were excluded. Review of the electronic medical record was undertaken to obtain detailed information on lines of treatment prior to EE, EE dosing and reason for EE discontinuation. The cohort was described and analyzed in total and by prior CDK4/6 inhibitor exposure. Time on treatment (TOT) was defined as start of EE to last dose or June 11, 2018 (censoring for data extraction) and was calculated using the Kaplan Meier method. The log rank test was used to compare TOT. Results: There were 110 patients extracted and 88 eligible for analysis (3 excluded for HER2+ disease, 14 for receipt of <1 cycle EE and 5 for participation on a placebo controlled trial of hormonal therapy +/- CDK4/6 inhibitor prior to EE. Median age 62.4 years (range 32.1-86.6 years). EE was administered first line in 12.5%, second line in 46.6% and third or greater line in 40.9%. Median time from start of first line therapy to start of EE was 19.3 months (range 0.3-72.1 months). Visceral metastases at start of EE in 62.5%. EE mean starting dose 7.3 mg (SD 2.5 mg) and mean last dose recorded 7.0 mg (SD 2.7 mg). At time of data extraction, 69 patients had stopped EE, 68.1% for progression and 31.9% for toxicity or other reason. Twenty patients had hormonal therapy + CDK4/6 inhibitor prior to EE. In the first line setting, 10 patients had letrozole and palbociclib. In the second line setting or greater, 5 patients had letrozole + palbociclib, 1 patient had tamoxifen + palbociclib and 4 patients had fulvestrant + palbociclib. Median time on hormonal therapy + CDK4/6 inhibitor was 12.0 months (range 4.0-20.9 months). Those with hormonal therapy + CDK4/6 inhibitor were more likely to have visceral metastases (p=0.02). Median time on treatment for the CDK4/6 exposed vs naïve groups was similar (5.8 vs 5.3 months, p=0.952). Median overall survival not yet reached. Conclusion: In a cohort of patients who have progressed on hormonal therapy + CDK4/6 inhibitor within 2 years, subsequent EE is a clinically meaningful treatment option in the setting of HR-positive/HER2-negative metastatic breast cancer. TOT was similar for CDK4/6 inhibitor exposed and naïve patients. Citation Format: Lupichuk SM, Recaldin B, Nixon NA, Mututino A, Joy AA. Real-world experience using exemestane and everolimus in patients with hormone receptor positive/HER2 negative breast cancer with and without prior CDK4/6 inhibitor exposure [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-13-06.

Background: We investigated utility of pre-treatment estrogen PET scans using 16α[18F]-fluoroestradiol PET (FES-PET) to predict hormone sensitivity in ER positive metastatic breast cancer. We evaluated FES discordance to routine [18F]-fluorodeoxy-D-glucose (FDG) PET and to pathologic characteristics of the primary including grade, ER/PgR levels, HER2 and Ki67 to assess prediction to hormone therapy response. Materials and Methods: Scans were performed prior to 1st, 2nd or 3rd line hormone therapy. Image review was double blinded to treatment and outcome using standard uptake values (SUV) and a tumor present scale from 1=def neg to 5=def pos. Clinicians were aware of FDG results but not FES. Standard radiological investigations were done per clinician choice. We established the percentage of metastatic sites that retained hormone sensitivity (FES positive) and compared this to the total number of FDG positive sites for each patient. Primary tumors were tested by immunochemistry for ER (SP1) PgR (PgR 636), HER2 (CerB-II) and Ki67 (MIB-1). Where HER2 was 2+ or 3+ CISH (CAP/ASCO guidelines) was also used. All tumors underwent pathology assessment (CAP-approved protocol). Results: N=38 mean age 53. Adjuvant chemo and hormones were given in 63.2%. At initial diagnosis 42.1% were stage 2, 21% were stage 4. 58% had visceral disease. 39.5%, 44.7% and 15.8% were starting 1st,2nd and 3rd line hormones. 53% (N=20) had discordance where FES showed fewer lesions in visceral/soft tissue/nodes/bone than FDG. Response to hormones was unsuccessful in the site of discordance in 50% (N=10). Of these N= 5 in liver +/− lung/nodes/bone N=1 in lung and N=4 in bone. Another 25% (N=5) had early progression but not in the discordant site. For 25% disease remained stable, mainly bone only disease where discordance was in non-bone sites and only bone scans were done for follow up. Overall all 7 HER2 positive cases (and 6 of 7 did not respond to hormones) and 6 of 7 grade 3 cases were in the discordant group (p=0.01 for HER2 and p=0.05 for grade 3 in the discordant group compared to the rest of the patients). There was no relationship between the level of ER positivity and FES scan discordance or response. Ki67 N=22 so far correlates only with HER2 (p=0.027). Of the 18 patients with no discordance of FES and FDG 14 had either SD or better responses. In 21% (N=8) FDG also revealed unsuspected visceral disease that required change to chemotherapy in N=4. Discussion: FES can help predict response to hormonal therapy for metastatic ER positive breast cancer. Not all lesions can be biopsied so optimum determination of hormonal response has not been established. Since HER2 + patients form a large group of non-responders these presumed luminal B patients may not be suitable for hormonal therapy even though they have ER+ primary disease. In 75% of women where there is discordance of FDG and FES the FES scan can predict early progression of disease on hormones. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD05-04.

Background: PAL , an oral cyclin dependent kinase (CDK) 4/6 inhibitor, is under investigation in multiple oncologic clinical trials and is currently approved for use in multiple countries in patients with hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2–) advanced breast cancer (ABC). International Conference on Harmonization guidance recommends that all new drugs be evaluated for effects on cardiac repolarization in a well-controlled clinical study. For drugs for which such evaluation cannot be conducted in healthy volunteers (eg, most non-adjuvant anticancer agents), collection of robust corrected QT (QTc) interval data from a dedicated QTc study (hybrid thorough QT/QTc study) in patients [pts] is required in the registration dossier. The phase 3 PALOMA-2 study (N=666) confirmed the superior clinical benefit of PAL+LET vs placebo (P) + LET in postmenopausal women with estrogen receptor positive/HER2– ABC who have not received any prior systemic anticancer therapies for ABC. One of the secondary objectives of the study was to evaluate the effects of PAL+LET on QTc. Methods: 12 lead (with a 10 second rhythm strip) tracings were performed in triplicate ∼2 min apart but within 10 min for all 3 ECGs. On the day preceding the initiation of treatment (Day 0), triplicate ECGs were obtained at time 0, 2, 4, 6, and 8 hrs (baseline). On Cycle 1 Day 14, when PAL concentrations were at steady-state, triplicate ECGs time-matched to baseline ECGs collected on Day 0 (±35 min) were obtained following PAL or P dosing. All ECGs were sent to a central laboratory for blinded manual adjudication and these data were used for analysis. ECG measurements included PR interval, QT interval, RR interval and QRS complex. The QT interval was corrected for the effect of heart rate using Fridericia's correction (QTcF), Bazett's correction (QTcB), and a study-specific correction factor (QTcS). Approximately 60 pts were to be included for QTc evaluation to ensure 40 evaluable pts in the PAL+LET arm (2:1 randomization) of PALOMA-2 and thus, to establish noninferiority between post-baseline and baseline (ΔQTc) at all 5 QTc sampling timepoints on Cycle 1 Day 14 with 90% power. The test was based on a 1-sided difference in means t test for paired ΔQTc (α= 0.05). The difference in means between ΔQTc under the alternative hypothesis is 10 ms, assuming a noninferiority margin of 20 ms and the standard deviation of the paired differences equal to 16 ms based on PALOMA-1 study. If the upper bounds (UB) of 1-sided 95% confidence intervals (CI) of ΔQTc for all 5 QTc time points were <20 ms, the post-baseline QTc will be considered noninferior to baseline and PAL+LET effect on QTc will be concluded to be not of clinical relevance. Results: A total of 77 pts were enrolled for intensive QTc assessment in PAL+LET arm. No pts had a post-baseline absolute maximum QTcF, QTcS or QTcB ≥500 ms or a ΔQTc ≥60 ms during the intensive QTc assessment period. A random effect analysis of the mean ΔQTc data demonstrated that the UB of the 1-sided 95% CI for QTcF, QTcS, and QTcB were <8 ms at all 5 QTc sampling time points. Conclusion: PAL+LET does not have a clinically relevant effect on QTc. Sponsor: Pfizer Citation Format: Ruiz A, Gauthier E, Durairaj C, Huang X, Hoffman J, Finn RS, Moulder S, Joy AA, Ettl J, Rugo HS, Wang D. Evaluation of the effects of palbociclib (PAL) + letrozole (LET) on QTc [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-22-10.