G1 Therapeutics Presents Phase 1 Data at ASCO Describing Favorable Safety Profile and Evidence of Antitumor Activity of Rintodestrant Combined with Palbociclib in Patients with ER+/HER2- Advanced Breast Cancer
- Combination of Rintodestrant and Palbociclib was Very Well Tolerated with No Reported Discontinuations due to Treatment-Emergent Adverse Events (TEAEs) -
- 60% Clinical Benefit Rate Achieved in Full Analysis Set at Week 24 -
“Between 30% and 50% of estrogen-positive tumors become resistant to selective estrogen receptor modulators (SERMs), so it is imperative that new and well tolerated approaches to overcoming resistance and improving response rates are developed,” said
The Phase 1, first-in-human, open-label study evaluated rintodestrant in women with ER+/HER2- advanced breast cancer after progression on endocrine therapy. The study comprised three parts: dose escalation of monotherapy rintodestrant (part 1), dose expansion of monotherapy rintodestrant (part 2), and rintodestrant in combination with palbociclib therapy (part 3). The results of part 1 and 2 were presented at the 2020 San Antonio Breast Cancer Symposium (SABCS) (2020 poster). Forty participants in the third part of the study received 800 mg of continuous rintodestrant once daily combined with 125 mg of palbociclib once daily for 21 days in 28-day cycles. This patient population had received a high degree of prior chemotherapy in the advanced setting (48%) and had visceral disease (68%); these tend to be patients that respond less well to CDK4/6 inhibitors in combination with endocrine therapies (ETs). The primary objective was safety and tolerability of rintodestrant with palbociclib, and the secondary objective was antitumor activity, including best overall response, progression-free survival (PFS), overall survival and clinical benefit rate, among other parameters.
Key study findings with a median duration of treatment of 6.2 months in the ongoing Phase 1 combination trial presented in the poster include:
- Rintodestrant combined with palbociclib was very well tolerated, with no rintodestrant-related serious adverse events (SAEs) or dose-reductions reported.
- The addition of rintodestrant to palbociclib did not result in additional or more severe toxicities, in particular, nausea, vomiting, or diarrhea.
- The most common treatment-emergent adverse events (TEAEs) of neutropenia and leukopenia are consistent with the known safety profile of palbociclib, as previously reported.
- No discontinuations or deaths due to TEAEs were reported.
- One case (3%) each of diarrhea and fatigue was reported, but neither was considered related to the rintodestrant/palbociclib.
- The clinical benefit rate (CBR) doubled from 30% to 60% when palbociclib was added to rintodestrant, suggesting the potential for favorable antitumor activity in patients with ER+/HER2- advanced breast cancer, including in patients with tumors harboring ESR1 variants.
- The CBR among patients with early relapse (first metastatic recurrence while on adjuvant ET for at least 2 years’ duration, or within 12 months of completing adjuvant ET) was 73% (8/11).
- In the full analysis set, 65% of patients experienced stable disease (SD).
- Median progression-free survival was 7.4 months (95% CI: 3.7 not reached), although the data are not yet mature as of the cutoff date (
April 7, 2021).
The Company is in the process of evaluating partnering options for rintodestrant.
G1 Therapeutics™ and the
This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as "may," "will," "expect," "plan," "anticipate," "estimate," "intend" and similar expressions (as well as other words or expressions referencing future events, conditions or circumstances) are intended to identify forward-looking statements. Forward-looking statements in this press release include, but are not limited to, those relating to expectations for the therapeutic potential of rintodestrant, and the possibility to realize the economic impact in the US market presented in the scientific analyses described above, and rintodestrant may fail to achieve the degree of market acceptance for commercial success, are based on the company’s expectations and assumptions as of the date of this press release. Each of these forward-looking statements involves risks and uncertainties. Factors that may cause the company’s actual results to differ from those expressed or implied in the forward-looking statements in this press release are discussed in the company’s filings with the
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