Design of SERENA-6, a phase III switching trial of camizestrant in ESR1-mutant breast cancer during first-line treatment

ESR1 mutation (ESR1m) is a frequent cause of acquired resistance to aromatase inhibitor (AI) plus cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i), which is a first-line therapy for hormone-receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC). Camizestrant is a next-generation oral selective estrogen receptor degrader (SERD) that in a phase II study significantly improved progression-free survival (PFS) over fulvestrant (also a SERD) in ER+/HER2- ABC. SERENA-6 (NCT04964934) is a randomized, double-blind, phase III study evaluating the efficacy and safety of switching from an AI to camizestrant, while maintaining the same CDK4/6i, upon detection of ESR1m in circulating tumor DNA before clinical disease progression on first-line therapy for HR+/HER2- ABC. The aim is to treat ESR1m clones and extend the duration of control of ER-driven tumor growth, delaying the need for chemotherapy. The primary end point is PFS; secondary end points include chemotherapy-free survival, time to second progression event (PFS2), overall survival, patient-reported outcomes and safety.

Expanding control of the tumor cell cycle with a CDK2/4/6 inhibitor

The CDK4/6 inhibitor, palbociclib (PAL), significantly improves progression-free survival in HR⁺/HER2^- breast cancer when combined with anti-hormonals. We sought to discover PAL resistance mechanisms in preclinical models and through analysis of clinical transcriptome specimens, which coalesced on induction of MYC oncogene and Cyclin E/CDK2 activity. We propose that targeting the G₁ kinases CDK2, CDK4, and CDK6 with a small-molecule overcomes resistance to CDK4/6 inhibition. We describe the pharmacodynamics and efficacy of PF-06873600 (PF3600), a pyridopyrimidine with potent inhibition of CDK2/4/6 activity and efficacy in multiple in vivo tumor models. Together with the clinical analysis, MYC activity predicts (PF3600) efficacy across multiple cell lineages. Finally, we find that CDK2/4/6 inhibition does not compromise tumor-specific immune checkpoint blockade responses in syngeneic models. We anticipate that (PF3600), currently in phase 1 clinical trials, offers a therapeutic option to cancer patients in whom CDK4/6 inhibition is insufficient to alter disease progression.

Hormonal treatment combined with targeted therapies in endocrine-responsive and HER2-positive metastatic breast cancer

Approximately 50% of HER2 positive breast cancer cases are also estrogen receptor (ER) positive. Data supports a role for close cross-talk between the ER and HER2 signaling pathways as an important contributor to the development of de novo or acquired resistance to hormone therapies. Therefore a strategy that simultaneously blocks both signaling pathways is a reasonable approach to prevent or overcome either endocrine or anti-HER2 therapy resistance. Moreover, preclinical data support the idea that PI3K inhibitors and CDK4/6 could be an attractive target that functions downstream of both ER and HER2 pathways. We conducted a literature review of the results of phase II and III studies testing targeted therapies in metastatic breast cancer with HER2-positive and hormonal-receptor-positive disease. The analyses included efficacy and toxicity data from earlier studies with a single anti-HER2 drug combined with hormonal therapy up to more recent studies testing new molecules targeting these signaling pathways. The aims of this review are to summarize current knowledge and to discuss research development including the possibility to spare chemotherapy in this subgroup of HER2-positive breast cancer patients.

Prognostic relevance of DNA damage and repair biomarkers in elderly patients with hormone-receptor-positive breast cancer treated with neoadjuvant hormone therapy: evidence from the real-world setting

Background:

The logic behind the outcome of endocrine therapy in breast cancer has long remained poorly understood. The prognostic role of DNA damage and repair biomarkers (DDR) was explored in postmenopausal, hormone-receptor-positive breast cancer patients treated with neoadjuvant hormone therapy (NAHT).

Methods:

Data on 55 patients were included. The phosphorylated ataxia-teleangectasia and Rad3-related protein (pATR), phosphorylated ataxia-telangiectasia mutated (ATM) kinase, and phosphorylated H2A Histone Family Member X (γ-H2AX) were evaluated by immunohistochemistry in paired tissues collected at baseline and following NAHT. Biomarkers were considered both singularly and within signatures. Ki-67 percentage change was the primary biomarker endpoint. Classical endpoints were also considered.

Results:

The most favorable Ki-67 outcome was associated with the γ-H2AX/pATM signature (p = 0.011). In models of Ki-67 reduction, ‘luminal B’ subtype, higher grade of anaplasia, and the γ-H2AX/pATM signature tested as significant (p < 0.05 for all). Results were confirmed in multivariate analysis. No association was observed with pathologic response. An increase of ∆γ-H2AX in paired breast tissues was associated with longer event-free survival (p = 0.027) and overall survival (p = 0.042). In Cox models, both survival outcomes were solely affected by grade of anaplasia, with less favorable prognosis in the highest grades (p < 0.05 for both).

Conclusions:

We report novel evidence of the prognostic role of DDR biomarkers on important patient outcomes in postmenopausal hormone-receptor-positive breast cancer patients treated with NAHT. If confirmed in future and adequately sized trials, our results may help inform therapeutic decisions and clarify underlying biological mechanisms.

Clinicopathologic features of hormone-receptor-positive breast cancer patients with late recurrence

The number of long-term breast cancer survivors with a risk of late recurrence is increasing. Hormone-receptor-positive patients have greater risks of late recurrence. Although several studies demonstrated that extended adjuvant endocrine therapy reduces the incidence of late recurrence, it remains unclear which hormone-receptor-positive patients have greater risks of late recurrence. Hormone-receptor-positive breast cancer patients were retrospectively selected from the prospective database of primary breast cancer patients treated at Keio University Hospital from January 1989 to December 2003. Late recurrence was defined as initial recurrence after 5 years from the initial surgery. We evaluated the clinicopathologic features of breast cancer patients with late recurrence. At a median follow-up of 10.9 years (range, 5.1-23.8), 371 patients had no recurrence, 90 had early recurrence (within 5 years), and 83 had late recurrence. Multivariate analysis revealed that >4 involved lymph nodes were significant risk factors for late recurrence (P < .001), whereas 1-3 positive nodes were not. Endocrine therapy significantly reduced the incidence of late recurrence (P < .001). After menopause, adjuvant therapy with aromatase inhibitors resulted in longer disease-free survival than tamoxifen (10-year disease-free survival: 97.6% vs 89.7%, P = .0955). High nodal involvement was significantly correlated with late recurrence in hormone-receptor-positive breast cancer patients. Hormone-receptor-positive breast cancer patients who receive adjuvant endocrine therapy with tamoxifen alone might be candidates for extended endocrine therapy.

Everolimus plus exemestane for hormone-receptor-positive, human epidermal growth factor receptor-2-negative advanced breast cancer: overall survival results from BOLERO-2†

BACKGROUND

The BOLERO-2 study previously demonstrated that adding everolimus (EVE) to exemestane (EXE) significantly improved progression-free survival (PFS) by more than twofold in patients with hormone-receptor-positive (HR(+)), HER2-negative advanced breast cancer that recurred or progressed during/after treatment with nonsteroidal aromatase inhibitors (NSAIs). The overall survival (OS) analysis is presented here.

PATIENTS AND METHODS

BOLERO-2 is a phase III, double-blind, randomized international trial comparing EVE 10 mg/day plus EXE 25 mg/day versus placebo (PBO) + EXE 25 mg/day in postmenopausal women with HR(+) advanced breast cancer with prior exposure to NSAIs. The primary end point was PFS by local investigator assessment; OS was a key secondary end point.

RESULTS

At the time of data cutoff (3 October 2013), 410 deaths had occurred and 13 patients remained on treatment. Median OS in patients receiving EVE + EXE was 31.0 months [95% confidence interval (CI) 28.0-34.6 months] compared with 26.6 months (95% CI 22.6-33.1 months) in patients receiving PBO + EXE (hazard ratio = 0.89; 95% CI 0.73-1.10; log-rank P = 0.14). Poststudy treatments were received by 84% of patients in the EVE + EXE arm versus 90% of patients in the PBO + EXE arm. Types of poststudy therapies were balanced across arms, except for chemotherapy (53% EVE + EXE versus 63% PBO + EXE). No new safety concerns were identified.

CONCLUSIONS

In BOLERO-2, adding EVE to EXE did not confer a statistically significant improvement in the secondary end point OS despite producing a clinically meaningful and statistically significant improvement in the primary end point, PFS (4.6-months prolongation in median PFS; P < 0.0001). Ongoing translational research should further refine the benefit of mTOR inhibition and related pathways in this treatment setting.

TRIAL REGISTRATION NUMBER

NCT00863655.