Data Support Switching CDK Inhibitors in Absence of Mutations
Switching CDK inhibitors to abemaciclib plus endocrine therapy significantly prolonged progression-free survival compared with endocrine therapy alone, with especially pronounced improvement in those without visceral metastases and those with longer durations of first-line CKD4/6 inhibitor therapy, said Ruth O’Regan, MD, of the University of Rochester, New York, who served as the discussant for the new research.
Dr. Regan referenced the improvement with abemaciclib in the BICR, a technique used to identify potential bias introduced by the assessment of local investigators. This can result in more favorable PFS on a treatment arm as seen in this study, but its use generally does not impact overall trial results, she said.
In the context of other studies involving switching CDK 4/6 inhibitors post-progression, the difference of 0.7 months in PFS between the abemaciclib and placebo groups was less than the 2.5 months difference seen in the MAINTAIN trial and the 1.3 months difference seen in the PALMIRA trial, Dr. O’Regan said in her presentation. Conversely, in the PACE trial, the intervention group did worse (4.6 months) than the control group in terms of the PFS (4.8 months), she said. Overall, the results of the postMONARCH trial support the use abemaciclib in patients with no actionable genetic mutation, she said.
In a question-and-answer session, Dr. Kalinsky was asked whether clinicians should still bother with genetic testing, since patients in the current study showed benefits regardless of the presence or absence of a mutation.
“I would still recommend that we check for mutations,” he emphasized. The current study “is one chapter in a much larger book,” and the field continues to evolve, he said.
A Clinician’s Take
“Currently, no standard second-line treatment after progression on first line CDK4/6 inhibitor plus endocrine therapy exists,” Malinda T. West, MD, of the University of Wisconsin, Madison, said in an interview. “Using a different CDK4/6 inhibitor after progression on a first CDK4/6 inhibitor has mixed data,” she said.
“If benefit with a second CDK4/6 inhibitor is confirmed, it may represent an additional low toxicity, chemotherapy-sparing regimen,” she noted.
Earlier data from the MAINTAIN trial had shown benefit with using ribociclib after progression on a primarily first line palbociclib, though other trials looking at use of palbociclib after progression on CDK 4/6 inhibitor [including the PACE and PALMIRA trials] had not, she said.
Overall, the results from postMONARCH support that switching the CDK4/6 inhibitor at progression to ribociclib or abemaciclib may be another treatment option, and reasonable for patients who don’t have other actionable mutations, Dr. West told this news organization.
The study was supported by Eli Lilly. Dr. Kalinsky disclosed that immediate family members are employed by EQRx and GRAIL, with stock or other ownership interests in these companies. He disclosed consulting or advisory roles with 4D Pharma; AstraZeneca; Cullinan Oncology; Daiichi Sankyo/AstraZeneca; eFFECTOR Therapeutics; Genentech/Roche; Immunomedics; Lilly; Menarini Silicon Biosystems; Merck; Mersana; Myovant Sciences; Novartis; Oncosec; Prelude Therapeutics; Puma Biotechnology; RayzeBio; Seagen; and Takeda. Dr. Kalinsky further disclosed research funding to his institution from Ascentage Pharma; AstraZeneca; Daiichi Sankyo; Genentech/Roche; Lilly; Novartis; and Seagen, and relationships with Genentech and Immunomedics.
Dr. O’Regan disclosed honoraria from AstraZeneca/MedImmune; bioTheranostics; Gilead Sciences; Novartis; Pfizer; Puma Biotechnology; and Seagen, serving as a consultant or adviser for AstraZeneca/MedImmune; bioTheranostics; Lilly; Novartis; Puma Biotechnology; and Seagen, and funding to her institution from Novartis and Puma Biotechnology.
Dr. West, who was not involved in the new research or other studies mentioned in this article, had no financial conflicts to disclose.