Jointly sponsored by Postgraduate Institute for Medicine and Clinical Care Options, LLC Clinical Focus: Current Approaches to the Treatment of Hormone Receptor–Positive, HER2-Negative Metastatic Breast Cancer This program is supported by an educational grant from Image: National Cancer Institute/Copyright©2012 Photo Researchers, Inc. All Rights Reserved

Endocrine Therapies for Breast Cancer Year Agent Mechanism 1977 SERMs Tamoxifen Toremifene Antagonizes estrogen receptor in breast tissue 1990s AIs Anastrozole Exemestane Letrozole Inhibit estrogen production in postmenopausal women 2000s ERD Fulvestrant Impairs ER dimerization, increases ER degradation, and disrupts nuclear localization of ER AI, aromatase inhibitor; ER, estrogen receptor; ERD, estrogen receptor downregulator; SERM, selective estrogen receptor modulator. 1. Lim E, et al. Oncology (Williston Park). 2012;26:688-694. 2. Croxtall JD, et al. Drugs. 2011;71:363-380.

Initial Treatment of HR-Positive Advanced Breast Cancer AIs are the current standard of care for initial treatment of postmenopausal women with HR-positive advanced breast cancer AIs have demonstrated improved efficacy compared with tamoxifen TTP, anastrozole vs tamoxifen: 10.7 vs 6.4 mos[6] TTP, letrozole vs tamoxifen: 9.4 vs 6.0 mos[5] PFS, exemestane vs tamoxifen: 9.9 vs 5.8 mos[7] Fulvestrant has demonstrated improved efficacy compared with anastrozole TTP, fulvestrant vs anastrozole: 23.4 vs 13.1 mos[8] Fulvestrant has demonstrated similar efficacy compared with tamoxifen[9] Combination fulvestrant and anastrozole was not more efficacious than anastrozole alone[10] AI, aromatase inhibitor; HR, hormone receptor; PFS, progression-free survival; TTP, time to progression. 6. Bonneterre J, et al. Cancer. 2001;92:2247-2258. 5. Mouridsen H, et al. J Clin Oncol. 2003;21:2101-2109. 7. Paridaens RJ, et al. J Clin Oncol. 2008;26:4883-4890. 8. Robertson FJ, et al. Breast Cancer Res Treat. 2012;136:503-511. 9. Howell A, et al. J Clin Oncol. 2004;22:1605-1613. 10. Mehta RS, et al. N Engl J Med 2012;367:435-444.

Resistance to Endocrine Therapy Complex interconnecting signaling pathways regulate cellular response to estrogen[13,14] May contribute to various mechanisms of resistance Resistance may be described as[15] Intrinsic or de novo: tumor does not respond to a drug from the onset of therapy Acquired: tumor that initially responded to therapy resumes growing Interconnectivity of pathways offers opportunities and challenges for combining therapies 13. Chang J, et al. Anticancer Agents Med Chem. 2012;[Epub ahead of print]. 14. Roop RP, et al. Future Oncol. 2012;8:273-292. 15. Hurvitz SA, et al. Cancer. 2008;113:2385-2397.

Progression on Endocrine Therapy in HR-Positive Advanced Breast Cancer 50% of patients with HR-positive advanced breast cancer will respond to initial endocrine treatment but will eventually relapse Multiple mechanisms allow for development of resistance to antiestrogen therapy Delaying systemic chemotherapy is the preferred therapeutic strategy Adding a second antiestrogen to inhibit the estrogen receptor pathway does not improve outcome Inhibition of both estrogen receptor and progrowth/antiapoptotic cell signaling pathways (eg, PI3K/AKT/mTOR) may improve therapeutic outcomes ER, estrogen receptor; HR, hormone receptor; PI3K, phosphoinositide 3-kinase; mTOR, mammalian target of rapamycin. 16. Di Leo A, et al. J Clin Oncol. 2010;28:4594-4600. 17. Chia, S, et al. J Clin Oncol. 2008;26:1664-1670. 18. Johnston SR, et al. European Breast Cancer Conference 2012. Abstract LBA2.

Crosstalk Between ER and PI3K/AKT/mTOR Signaling: Rationale for Dual Inhibition PTEN mTOR RAS RAF MEK MAPK ER target gene transcription P EGFR HER2 E ER mTOR activates ER in a ligand-independent manner Estradiol suppresses apoptosis induced by mTOR blockade Hyperactivation of the mTOR pathway is observed in endocrine therapy–resistant breast cancer cells AKT, protein kinase B; E, estrogen; EGFR, epidermal growth factor receptor; ER, endocrine receptor; HER2, human epidermal growth factor receptor-2; MAPK, mitogen-activated protein kinase; mTOR, mammalian target of rapamycin. 6

BOLERO-2: Exemestane ± Everolimus in Nonsteroidal AI–Refractory ABC Postmenopausal women with HR-positive, HER2-negative advanced breast cancer refractory to letrozole or anastrozole (N = 724) Everolimus 10 mg/day + Exemestane 25 mg/day (n = 485) Placebo + Exemestane 25 mg/day (n = 239) Refractory to therapy: Recurrence during or within 12 mos of end of adjuvant treatment Progression during or within 1 mo after end of treatment for advanced disease Stratification: Sensitivity to previous hormonal therapy Presence of visceral disease No crossover allowed Primary endpoint: PFS Secondary endpoints: OS, ORR, CBR, safety, QoL, bone markers ABC, advanced breast cancer; AI, aromatase inhibitor; CBR, clinical benefit rate; OS, overall survival; ORR; overall response rate; PFS, progression-free survival; QoL, quality of life. 25. Baselga J, et al. N Engl J Med. 2012;366:520-529.

BOLERO-2: Baseline Characteristics Everolimus + Exemestane (n = 485) Placebo + Exemestane (n = 239) Metastatic site Liver Lung Bone 33 29 76 30 33 77 Number of metastatic sites 1 2 ≥ 3 32 31 36 29 34 37 Visceral disease 56 Measurable disease* 70 68 *All other patients had ≥ 1 lytic bone lesion 26. Baselga J, et al. N Engl J Med. 2012;366:520-529

BOLERO-2: PFS at 18-Mo Follow-up 100 Median PFS, Mos EVE + EXE: 7.82 PBO + EXE: 3.19 Hazard ratio: 0.45 (95% CI: 0.38-0.54; log-rank P < .0001) Censoring times EVE + EXE (n/N = 310/485) PBO + EXE (n/N = 200/239) 80 60 Probability of Event (%) 40 20 CI, confidence interval; EVE, everolimus; EXE, exemestane; PBO, placebo. 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 102 108 114 120 Wk Patients at Risk, n EVE + EXE 485 436 366 304 257 221 185 158 124 91 66 50 35 24 22 13 10 8 2 1 PBO + EXE 239 190 132 96 67 50 39 30 21 15 10 8 5 3 1 1 1 28. Piccart-Gebhart M, et al. ASCO 2012. Abstract 559.

BOLERO-2: Adverse Events at 18-Mo Follow-up Everolimus + Exemestane (n = 482) Placebo + Exemestane (n = 238) Grade All 3 4 Total 100 44 9 91 23 5 Stomatitis 59 8 12 < 1 Rash 39 1 7 Fatigue 37 27 Diarrhea 34 2 19 Nausea 31 29 Appetite decreased 13 Noninfectious pneumonitis 16 Hyperglycemia 14 29. Piccart-Gebhart M, et al. ASCO 2012. Abstract 559.

Everolimus: Adverse Effects Noninfectious pneumonitis Reported in 11% to 14% of patients treated with everolimus[1] Onset typically occurs within 2-6 mos of initiating therapy Infections Immunosuppressive properties Opportunistic infection: pneumonia and other bacterial and fungal infections Reported in up to 37% of the patients studied in everolimus clinical trials Patients should avoid live vaccines and close contact with those who have received live vaccines Potential for viral reactivation: hepatitis B, others 30. Everolimus [package insert].

Current Guidelines for Endocrine Therapy in Advanced Breast Cancer Previous Endocrine Therapy Within 1 Yr Premenopausal Ovarian ablation + ET Postmenopausal Second-line ET Visceral metastasis Consider initial chemotherapy No Endocrine Therapy Within 1 Yr Ovarian ablation + ET or antiestrogen AI or antiestrogen Second-line endocrine therapy for all subsequent treatment Patients with bone disease should be treated with bone-targeted therapy Consider the addition of everolimus to exemestane in postmenopausal women who are resistant to nonsteroidal AIs AI, aromatase inhibitor; ET, endocrine therapy. 31. NCCN. Clinical practice guidelines in oncology: breast cancer. v.3.2012. 12

Factors That Guide Selection of Subsequent Lines of Therapy Disease burden Response to previous therapy Patient disease symptoms Visceral crisis Age

Available Classes of Therapy for ER+, HER2-Negative Postmenopausal Women Endocrine therapy Selective nonsteroidal AIs Steroidal AIs Pure antiandrogens Progestin High-dose estrogen therapy Selective estrogen receptor modulators Chemotherapy Taxanes Antimetabolites Anthracyclines Other microtubule inhibitors Targeted therapy AI, aromatase inhibitor; ER, estrogen receptor.

Combining Targeted and Antiestrogen Therapies in HR-Positive Breast Cancer EGFR HER2 E Aromatase Inhibitor Nonsteroidal AIs Anastrozole Letrozole Steroidal AIs Exemestane TKI E RAS PI3K PTEN ER Downregulator Fulvestrant RAF ER E mTOR Inhibitors Everolimus Sirolimus Temsirolimus AKT AI, aromatase inhibitor; E, estrogen; ER, estrogen receptor; HR, hormone receptor; mTOR, mammalian target of rapamycin; TKI, tyrosine kinase inhibitor. MEK MAPK mTOR Selective Estrogen Receptor Modulators Tamoxifen Toremifene CDK 4/6 Inhibitor PD 0332991 Cell Cycle ER target gene transcription ER E ER E HDAC Inhibitor Entinostat Transcription Silencing

Cyclin-Dependent Kinase 4/6 Inhibition as a Therapy in HR-Positive Breast Cancer CDK4/6 regulates passage of cells through the cell cycle[35] PD0332991 is an orally active CDK4/6 inhibitor that induces G0/G1 arrest Factors associated with PD0332991 sensitivity: luminal ER expression, elevated expression of cyclin D1 and Rb protein, and reduced p16 expression Synergistic with tamoxifen in vitro Phase I results of PD0332991 plus letrozole (N = 12)[36] Determination of recommended phase II dosing in combination with letrozole PD0332991 125 mg/day for 3 wks of a 4-wk cycle Letrozole 2.5 mg/day Most common adverse events included neutropenia, leukopenia, and fatigue AI, aromatase inhibitor; ER, estrogen receptor; HR, hormone receptor. 35. Finn RS, et al. Breast Cancer Res. 2009;11:R77. 36. Slamon DJ, et al. J Clin Oncol. 2010;28:3060. 38. Finn RS, et al. Cancer Res. 2012;72:S1-S6.

TRIO-18: Phase II, PD0332991 + Letrozole Part 1: ER-positive, HER2-negative breast cancer (N = 66) Exploratory biomarkers for p16 loss, cyclin D1 gene amplification did not improve over ER positivity alone as a selection marker Part 2: ER-positive, HER2-negative breast cancer with cyclin D1 gene amplification and/or p16 loss (N = 99) Median PFS: letrozole + PD0339921 vs letrozole: 26.1 vs 7.5 mos (hazard ratio: 0.37; 95% CI: 0.21-0.63; P < .001) Best Overall Response (ITT) PD0332991 + Letrozole (n = 84) Letrozole (n = 81) All randomized patients, n ORR, % 34 26 CR, % 1 PR, % 25 SD ≥ 24 wks, % 36 18 Clinical benefit rate, % 59 CI, confidence interval; CR, complete response; ER, estrogen receptor; ITT, intent to treat; ORR, overall response rate; PFS, progression-free survival; PR, partial response. 39. Finn RS, et al. Cancer Res. 2012;72:S1-S6.

HDAC Inhibitors Mechanism of Action HDAC inhibitors relax the structure of DNA making it more accessible to RNA polymerases Closed chromatin = genes off Histone acetyltransferases (HATs) Histone deacetylases (HDACs) Open chromatin = genes on HDAC inhibitors AC HAT, histone acetyl transferase; HDAC, histone deacetylase 40. Pathiraja TN, et al. J Mam Gland Biol Neoplasia. 2010;15:35-47.

Epigenetic Therapy With Entinostat Oral, isoform-selective HDAC inhibitor Long half-life (80-100 hrs) allows for weekly and biweekly dosing Targets cancer-relevant class 1 HDACs Well-characterized safety profile No evidence of cardiac toxicity ENCORE 301 trial randomized 130 postmenopausal women with ER- positive advanced breast cancer who progressed on previous nonsteroidal AI therapy Exemestane 25 mg/day + entinostat 5 mg/wk (n = 64) Exemestane 25 mg/day + placebo (n = 66) AML, acute myeloid leukemia; ER, estrogen receptor; HDAC, histone deacetylase. 42. Knipstein J, et al. Expert Opin Investig Drugs. 2011;20:1455-1467.

ENCORE 301: PFS, ORR, CBR[45] 1.00 PFS, Mos ORR, % CBR, % Placebo 2.27 4.6 25.8 Entinostat 4.28 4.7 26.6 Hazard ratio: 0.73 (95% CI: 0.49-1.09; 1-sided P = .06) 0.75 Progression Probability 0.50 0.25 2 4 6 8 10 12 14 16 18 CBR, clinical benefit rate; CI, confidence interval; HDAC, histone deacetylase; ORR, overall response rate; PFS, progression-free survival. Mos Placebo Entinostat 31/66 15/64 13/33 14/45 4/20 11/29 4/15 3/16 1/7 3/10 3/6 0/3 0/2 0/1 0/1 0/1 1/1 1/1 Analyses of patient samples, demonstrated an association of HDAC inhibitor–induced lysine hyperacetylation in circulating B, T, and monocyte cells with improved clinical outcome and may be useful biomarker for HDAC inhibitor action[46] 45. Klein P, et al. ASCO 2012 Breast Cancer Symposium. Abstract 128. 46. Ordentlich P. Mol Cancer Ther. 2011;10:Abstract PR-6.

Summary AIs have become the standard of care for initial treatment of postmenopausal women with HR-positive advanced breast cancer However, many patients with advanced breast cancer fail to respond initially and all patients eventually progress Patients progressing or recurring after initial endocrine therapy demonstrate low ORR and limited survival benefit due to endocrine resistance New treatments may overcome endocrine resistance and delay need for chemotherapy Combined targeting of both ER and growth factor receptor or intracellular signaling pathways may be promising treatment approach ER, estrogen receptor; HR, hormone receptor; ORR, overall response rate.