Safety and Efficacy of Tucatinib, Letrozole, and Palbociclib in Patients with Previously Treated HR+/HER2+ Breast Cancer

PURPOSE

To overcome resistance to antihormonal and HER2-targeted agents mediated by cyclin D1-CDK4/6 complex, we proposed an oral combination of the HER2 inhibitor tucatinib, aromatase inhibitor letrozole, and CDK4/6 inhibitor palbociclib (TLP combination) for treatment of HR+/HER2+ metastatic breast cancer (MBC).

PATIENTS AND METHODS

Phase Ib/II TLP trial (NCT03054363) enrolled patients with HR+/HER2+ MBC treated with ≥2 HER2-targeted agents. The phase Ib primary endpoint was safety of the regimen evaluated by NCI CTCAE version 4.3. The phase II primary endpoint was efficacy by median progression-free survival (mPFS).

RESULTS

Forty-two women ages 22 to 81 years were enrolled. Patients received a median of two lines of therapy in the metastatic setting, 71.4% had visceral disease, 35.7% had CNS disease. The most common treatment-emergent adverse events (AE) of grade ≥3 were neutropenia (64.3%), leukopenia (23.8%), diarrhea (19.0%), and fatigue (14.3%). Tucatinib increased AUC10-19 hours of palbociclib 1.7-fold, requiring palbociclib dose reduction from 125 to 75 mg daily. In 40 response-evaluable patients, mPFS was 8.4 months, with similar mPFS in non-CNS and CNS cohorts (10.0 months vs. 8.2 months; P = 0.9). Overall response rate was 44.5%, median duration of response was 13.9 months, and clinical benefit rate was 70.4%; 60% of patients were on treatment for ≥6 months, 25% for ≥1 year, and 10% for ≥2 years. In the CNS cohort, 26.6% of patients remained on study for ≥1 year.

CONCLUSIONS

TLP combination was safe and tolerable. AEs were expected and manageable with supportive therapy and dose reductions. TLP showed excellent efficacy for an all-oral chemotherapy-free regimen warranting further testing. See related commentary by Huppert and Rugo, p. 4993.

Phase II trial of fulvestrant plus enzalutamide in ER+/HER2- advanced breast cancer

This clinical trial combined fulvestrant with the anti-androgen enzalutamide in women with metastatic ER+/HER2- breast cancer (BC). Eligible patients were women with ECOG 0-2, ER+/HER2- measurable or evaluable metastatic BC. Prior fulvestrant was allowed. Fulvestrant was administered at 500 mg IM on days 1, 15, 29, and every 4 weeks thereafter. Enzalutamide was given at 160 mg po daily. Fresh tumor biopsies were required at study entry and after 4 weeks of treatment. The primary efficacy endpoint of the trial was the clinical benefit rate at 24 weeks (CBR24). The median age was 61 years (46-87); PS 1 (0-1); median of 4 prior non-hormonal and 3 prior hormonal therapies for metastatic disease. Twelve had prior fulvestrant, and 91% had visceral disease. CBR24 was 25% (7/28 evaluable). Median progression-free survival (PFS) was 8 weeks (95% CI: 2-52). Adverse events were as expected for hormonal therapy. Significant (p < 0.1) univariate relationships existed between PFS and ER%, AR%, and PIK3CA and/or PTEN mutations. Baseline levels of phospho-proteins in the mTOR pathway were more highly expressed in biopsies of patients with shorter PFS. Fulvestrant plus enzalutamide had manageable side effects. The primary endpoint of CBR24 was 25% in heavily pretreated metastatic ER+/HER2- BC. Short PFS was associated with activation of the mTOR pathway, and PIK3CA and/or PTEN mutations were associated with an increased hazard of progression. Thus, a combination of fulvestrant or other SERD plus AKT/PI3K/mTOR inhibitor with or without AR inhibition warrants investigation in second-line endocrine therapy of metastatic ER+ BC.

Abstract 2867: Laboratory analyses of metastatic ER+/Her2- breast cancer treated with fulvestrant plus enzalutamide

Background: The clinical implications of the androgen receptor (AR), particularly in the context of aromatase inhibitor (AI) refractory metastatic breast cancer (MBC) are unclear. While AR is associated with more indolent primary tumors, high AR relative to ER in primary breast cancer is associated with endocrine resistance, and in the absence of estradiol or low or blocked ER, AR can exert a pro-survival signal. In a phase II trial of fulvestrant plus enzalutamide in ER+/Her2- MBC we analyzed serial biopsies pre- and post-treatment

Methods: Eligible patients were women with ECOG 0-2, ER+/Her2- MBC. Fulvestrant 500 mg IM days 1, 15, 29 and every 4 weeks thereafter and Enzalutamide at 160 mg po daily on a continual basis were administered. Biopsies were required at study entry and at ~4 weeks on therapy. The clinical benefit rate at 24 weeks (CBR24) was the primary endpoint for efficacy. We performed mutational analysis to detect mutations including ESR1 exon 8 mutations.We examined estrogen, progesterone, androgen and glucocorticoid receptors, multiplex analysis of immune cells and PD-L1, and performed reverse phase protein array (RPPA) based protein pathway activation analysis of over 150 proteins/phosphoprotein drug targets from LCM-enriched tumor epithelium in baseline and post-treatment metastatic biopsies. Comparisons of PFS Responders (PFS longer than or equal to 24 weeks) and PFS Non-Responders (PFS shorter than or equal to 5 weeks) were performed using moderated t-tests on log2 transformed data.

Results: 32 were eligible and median age was 61 years (46-87); PS 1 (0-1); a median of 2 prior chemotherapy and 2 prior hormonal therapies for metastatic disease (including 7 with prior Fulvestrant) and 90% had visceral disease. ESR1 mutant metastases had higher levels of ER and PR than those with wild type ESR1 (p&lt;0.05). In a paired t test, ER and Ki67 decreased (p&lt;0.05) with treatment. RPPA analysis of the baseline biopsy sample indicated activation of mTOR pathway proteins associated with non-response, while phosphorylated RB, EGFR and IRS1 were associated with response (PFS greater than 24 weeks). ESR1 mutation positive metastases had significantly more T helper cells, T regulatory cells and macrophages than those with wild type ESR1.PD-L1 increased with treatment in all patients by paired t test (p&lt;0.03).

Conclusions: Clinical benefit lasting 6-12 months was observed in 23% of patients. Our studies show important differences in hormone receptor expression and immune infiltrates in ESR1 mutated disease. RPPA based pathway activation mapping showed that mTOR pathway activation was associated with shorter PFS (p&lt;0.05). Since PD-L1 expression significantly increased with treatment, we conclude that mTOR and/or PD-L1 directed therapies could be useful with Fulvestrant and Enzalutamide in patients with MBC refractory to current standard of care treatments

Citation Format: Jennifer K. Richer, Nicole S. Spoelstra, Alyse Winchester, Julia Wulfkuhle, Sharon B. Sams, Gregory Vidal, Peter Kabos, Jennifer Diamond, Elena Shagisultanova, Anosheh Afghahi, Jose Mayordomo, Tessa McSpadden, Gloria Crawford, Virginia Borges, Dexiang Gao, Emanuel Petricoin, Anthony D. Elias. Laboratory analyses of metastatic ER+/Her2- breast cancer treated with fulvestrant plus enzalutamide [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2867.

Abstract PS12-14: Phase II trial of fulvestrant plus enzalutamide in ER+/Her2- advanced breast cancer

Up to 91% of ER+ breast cancers express androgen receptor (AR), but its function is uncertain. Although AR expression is associated with more indolent tumors, high AR expression relative to ER is associated with endocrine resistance, and in the absence of estradiol or if ER function is blocked, preclinical studies suggest that AR can take over to signal cell survival and proliferation. Following extensive preclinical studies and a brief phase I to demonstrate a lack of significant PK interaction, this phase II trial of fulvestrant plus enzalutamide in ER+/Her2- metastatic breast cancer was conducted. Methods: Eligible patients were women with ECOG 0-2, ER+/Her2- measurable or evaluable metastatic breast cancer without CNS disease. Prior fulvestrant was allowed, if clinically indicated as per treating physician. Fulvestrant was administered in standard dosing at 500 mg IM days 1, 15, 29 and every 4 weeks thereafter. Enzalutamide was given at 160 mg po daily on a continual basis. Fresh tumor biopsies were required at study entry and at about 4 weeks on therapy. The primary efficacy endpoint of the trial was clinical benefit rate at 24 weeks (CBR24). Assuming the undesirable rate of 10% and desirable rate of 30%, a sample size of 24 provided 89% power to detect this 25% rate difference using an exact binomial test with a one-sided alpha of 0.085. Due to the exploratory nature of biomarker analysis, the type I error rate was not adjusted for exploring multiple biomarkers. Results: A total of 38 patients were consented, of whom 32 were eligible. Median age was 61 years (46-87); PS 1 (0-1); a median of 2 prior chemotherapy and 2 prior hormonal therapies for metastatic disease. Twelve patients had prior fulvestrant, and 90% had visceral disease. TEAEs &gt;20% included fatigue, nausea/vomiting, constipation, headache, anorexia, although most were low grade. There were no G4 or G5 toxicities. Median PFS was 2.0 months (0.5-12). CBR24 was 25% (7/28 evaluable).Conclusions: In a heavily pretreated population of women with metastatic ER+/Her2- BC, the combination of fulvestrant plus enzalutamide had manageable side effects, and modest activity. About 25% reached the primary endpoint of clinical benefit of more than 6 months on therapy. Extensive molecular studies of paired fresh biopsies from pretreatment and at 4 weeks are underway. These analyses and correlations with clinical outcome will be described.

Citation Format: Anthony D Elias, Nicole Spoelsta, Gregory A Vidal, Sharon Sams, Peter Kabos, Jennifer R Diamond, Elena Shagisultanova, Anosheh Afghahi, Jose Mayordomo, Tessa McSpadden, Gloria Crawford, Lisa Carter, Kathryn Zolman, Stephanie Armstead, Alyse Winchester, Virginia Borges, Julia Wulfkuhle, Emanuel Petricoin, Dexiang Gao, Jennifer Richer. Phase II trial of fulvestrant plus enzalutamide in ER+/Her2- advanced breast cancer [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 PS12-14.

Tucatinib, palbociclib, and letrozole in HR+/HER2+ metastatic breast cancer: Report of phase IB safety cohort

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Background: Based on preclinical synergy, we are conducting a phase IB/II clinical trial of tucatinib (HER2 small molecule inhibitor, T), palbociclib (CDK4/6 inhibitor, P) and letrozole (aromatase inhibitor, L) in HR+/HER2+ metastatic breast cancer (MBC). Methods: Post-menopausal, or pre-menopausal women on ovarian suppression, with prior ≥2 HER2 inhibitors at any time of disease; ≥1 HER2 inhibitor for MBC or front line bone/soft tissue only disease are eligible provided ≤2 endocrine agents for MBC. Prior CDK4/6 or HER2 small molecule inhibitors are not allowed. Treatment entails T 300 mg BID, P 125 mg/day 21 days on, 7 days off, and L 2.5 mg/day. Safety was assessed using CTCAE v.4.03 with standard definitions for dose limiting toxicity (DLT). Dose reductions of T and / or P for DLTs, and discontinuation of either P or L for toxicity were allowed at any time during the study. Safety thresholds were set as DLTs in ≤7/20 pts for T, ≤15/20 pts for P, or ≤14/20 pts attributable to both T and P. Results: Phase Ib enrolled 20 pts from 11/16/17 to 12/5/18. The median age is 53y (22-70y), median number of prior lines of MBC therapy is 2 (0-5). 70% of pts have visceral disease and 45% CNS disease. Prior treatment includes 100% of pts with trastuzumab and pertuzumab, and 45% of pts with prior TDM-1. One pt required dose reduction of T; 9 (45%) had dose reduction and 2 (10%) discontinued P for DLTs. One pt discontinued L. Safety boundaries were not crossed. The most common grade (G) ≥3 toxicities were neutropenia (G3 55%, G4 15%), diarrhea (G3 20%), infections (G3 20%), thrombocytopenia (G3 10%) and mucositis (G3 10%). The frequency and type of toxicities were consistent with those previously reported for each single agent. PK analysis showed no interaction between P and T. As of 1/4/19, 14 pts (70%) remain on study (5 pts for ≥6 months) and 6 pts removed for progression. No withdrawals for toxicity and no deaths on study. The longest time on study (ongoing) is 10 months for pts without CNS disease, and 6 months for pts with CNS disease. Conclusions: T, P, L combination showed an acceptable safety profile and encouraging antitumor activity. RP2D of T is 300mg PO BID in combination with full doses of P and L. Enrollment in phase II cohort is ongoing. Clinical trial information: NCT03054363.

Abstract OT1-03-06: Phase IB/II clinical trial to evaluate safety and efficacy of tucatinib in combination with palbociclib and letrozole in patients with hormone receptor positive and HER2-positive metastatic breast cancer

Breast cancers overexpressing HER2-oncogene and hormone receptors (HR) represent therapeutic challenge because of a bi-directional cross-talk between HR and HER2 pathways leading to tumor progression and drug resistance. There is a strong rationale for evaluation of novel targeted drug combinations in this breast cancer subtype.

We designed a phase IB /II clinical trial to test the combination of novel oral HER2 small molecule inhibitor tucatinib with CDK4/6 inhibitor palbociclib and aromatase inhibitor letrozole in patients with HR+/HER2+ metastatic breast cancer (NCT03054363). In addition to the rationale for the synergy of targeting HR, HER2 and CDK4/6 pathways simultaneously in this disease setting and its potential for anti-tumor efficacy, we propose this novel combination of three oral agents, if well tolerated, will be highly patient-centered as an effective non-chemotherapy based regimen for treatment of HR+/HER2+ breast cancer.

This multicenter clinical trial is conducted through the Academic Breast Cancer Consortium (ABRCC), with the University of Colorado Cancer Center as the lead site.

Target enrollment: 40 patients (20 patients in phase IB and 20 patients in phase II part).

Main inclusion criteria:

1. HR+/HER2+ locally advanced unresectable / metastatic breast cancer

2. Measurable or evaluable disease. Bone only disease is allowed.

3. Subjects without brain metastases are eligible; subjects with untreated asymptomatic CNS metastases not needing immediate local therapy, and subjects with stable brain metastases previously treated with radiation therapy or surgery are eligible

4. ECOG 0-1

5. Postmenopausal women, or premenopausal women on ovarian suppression

6. Prior treatments:

- At least two approved HER2-targeted agents (trastuzumab, pertuzumab, or TDM-1) at any time in the course of the disease

- At least 1 line of HER2-targeted therapy in the metastatic setting (with the exception of asymptomatic subjects with oligometastatic or bone / soft tissue only disease who, on investigator opinion, are appropriate for a front line single agent anti-endocrine therapy per NCCN guidelines)

- Up to 2 lines of prior endocrine therapy in the metastatic setting are allowed

7. Adequate organ and marrow function

Main exclusion criteria:

1. Previously treated progressing brain metastases

2. Brain metastases and contraindications to undergo contrast brain MRI

3. Toxicities of prior cancer therapies that have not resolved to grade 1 or less, except peripheral neuropathy, which must have resolved to grade 2 or less, and alopecia

4. Previous treatment with EGFR or HER2 tyrosine kinase inhibitors or CDK4/6 inhibitors

5. Systemic anti-cancer therapy or radiation within 2 weeks of the first dose of study drugs

6. Active bacterial, fungal or viral infections, hepatitis B, C, or HIV

7. Clinically significant cardio-vascular disease

Primary objectives:

- Phase IB: safety and tolerability of combination therapy

- Phase II: efficacy by PFS

Exploratory assessment of biomarkers of resistance and response will be performed in the blood and biopsy samples

Study contact: Elena Shagisultanova, MD, PhD, elena.shagisultanova@ucdenver.edu

Citation Format: Shagisultanova E, Diamond J, Stopeck A, Pusztai L, O'Regan R, Gradishar W, Brown-Glaberman U, Chalasani P, McSpadden T, Borakove M, Shedin T, Kabos P, Borges V. Phase IB/II clinical trial to evaluate safety and efficacy of tucatinib in combination with palbociclib and letrozole in patients with hormone receptor positive and HER2-positive metastatic breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT1-03-06.

Abstract A050: ARRY-380, an oral HER2 inhibitor: Final phase 1 results and conclusions

Background: Overexpression of HER2 occurs in ~25% of breast cancers. Despite the treatment successes achieved to date, improved clinical outcomes remain needed, including prevention and treatment of CNS metastases. Small-molecule HER2 inhibitors may have the advantage of being able to treat CNS and systemic disease simultaneously, particularly if used in combination with antibody-based therapy. However, currently available small molecules also target EGFR, with associated use limiting toxicities. Therefore, a specific small-molecule inhibitor of HER2 is needed. ARRY-380 is an oral, potent, reversible, ATP competitive, small molecule inhibitor of HER2. In cell-based assays, ARRY-380 was ~500-fold selective for HER2 versus EGFR. In multiple preclinical models, ARRY-380 demonstrated significant single agent and combination activity. In models of CNS disease, ARRY-380 was highly active as a single agent and demonstrated superior activity compared to lapatinib or neratinib. Thus, ARRY-380 was evaluated in a first in human clinical study.

Methods: A Phase 1 clinical study of ARRY-380 was conducted in patients with advanced solid tumors that are believed to express HER2, with both dose-escalation (25 to 800 mg BID) and MTD expansion components. ARRY-380 was administered BID in 28 day cycles. Safety was assessed by AEs, clinical laboratory test results, physical examinations, vital signs and ECGs. Tumor response was assessed by RECIST every 2 cycles. Serial PK assessments were conducted in Cycle 1 on Days 1 and 3 and at steady state on Day 15.

Results: A total of 50 patients were enrolled (33 dose-escalation and 17 expansion). These results focus on the 31 patients treated at doses ≥ MTD: 27 at the MTD of 600/650 mg BID and 4 at 800 mg BID. All 31 patients had HER2+ metastatic breast cancer (MBC) that had progressed on a prior trastuzumab containing regimen and 94% had received prior lapatinib, many who progressed on treatment. Dose limiting toxicity consisting of reversible Grade (G) 3 AST (n=1) and AST/ALT elevations (n=1) occurred in 2 of 4 patients treated at 800 mg BID, with an onset that occurred within 1 week, resolved within 2 weeks, and patients resumed treatment at a lower dose.

Overall, ARRY-380 demonstrated an acceptable safety profile at the MTD. The most common treatment-related AEs were nausea, diarrhea, fatigue, vomiting, liver enzyme elevations and rash, and were primarily G1 with a low incidence of G2 (gastrointestinal events [n=2], fatigue [n=3], liver enzyme elevations [n=2]) or G3 (rash [n=1], liver enzyme elevations [n=1]) events. There were no treatment-related cardiac events, serious AEs or G4 AEs.

ARRY-380 Cmax and AUC increased with increasing dose, with a Tmax of 2 hours and a t1/2 of 5 hours. Twenty-two HER2+ MBC patients with measurable disease were treated with ARRY-380 at doses ≥ 600 mg BID. In this heavily pretreated population, there was a clinical benefit rate (PR [n=3] plus SD for at least 6 months [n=3]) of 27%. Notably, 2 patients with PRs on ARRY-380 had confirmed progressions while on prior lapatinib- and trastuzumab-containing regimens.

Conclusions: ARRY-380 has demonstrated an acceptable safety and PK profile at the MTD. As predicted for a HER2-selective agent that does not inhibit EGFR, there was a very low incidence of Grade 2/3 rash and diarrhea. ARRY-380 has shown promising signs of antitumor activity in a heavily pretreated HER2+ MBC population. These safety and preliminary efficacy data support the continued clinical development of ARRY-380 at the recommended dose of 600 mg BID.

Citation Format: Virginia F. Borges, Steven K.L Chia, Susan D'Aloisio, Gina Fernetich, Bessie Sajan, Tessa McSpadden, Renae Chavira, Emma Barrett, Kari Guthrie, Jennifer Garrus, Tara Baetz, Stacy Moulder. ARRY-380, an oral HER2 inhibitor: Final phase 1 results and conclusions. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A050.