An objective response rate was seen in 45% of patients, with a further 51% achieving stable disease, for a disease control rate of 96%.
“The vast majority of patients had significant tumor shrinkage,” said study investigator Gregory J. Riely, MD, PhD, when presenting the results at the European Lung Cancer Virtual Congress 2021 (Abstract 990_PR).
Dr. Riely, vice chair of clinical research in the department of medicine at Memorial Sloan Kettering Cancer Center in New York, noted that just 6 of the 70 patients in this phase 1/2 trial showed evidence of measurable tumor growth.
“This new way of targeting an oncogene may very well represent an evolutionary step forward in the management of lung cancer patients, akin to when we first had EGFR inhibitors,” Alastair Greystoke, MBChB, PhD, said in his discussion of the trial.
Dr. Greystoke, a clinical senior lecturer and honorary consultant in medical oncology at Newcastle (England) University, observed that the availability of KRAS-targeting agents could have a large potential impact on clinical practice. They could add another 14% of patients with NSCLC to the list of those who are eligible for molecularly-targeted therapy.
“It may be that soon, almost half our patients with lung adenocarcinoma will have a potential targetable abnormality,” Dr. Greystoke said.
Data confirm KRAS as a therapeutic target
Adagrasib is now the second drug to show promise as an inhibitor of KRAS G12C. In a phase 2 trial, the KRAS inhibitor sotorasib produced a response rate of 37%, a median response duration of 10 months, and a median progression-free survival of 6.8 months in patients with NSCLC.
Data on response duration and progression-free survival are not yet available for adagrasib. However, the duration of response extended past 11 months in four of the six patients who achieved a partial response to adagrasib in the phase 1/1b portion of the KRYSTAL-1 trial.
“What we’ve seen from this data, and data with other agents, is that responses are very heterogeneous,” Dr. Greystoke observed. “A small number of patients do not respond at all. In some patients, responses are short-lived, whilst in other patients, responses are long and still ongoing.”
KRYSTAL-1 study design and safety
KRYSTAL-1 is an ongoing phase 1/2 study designed to assess the safety and clinical activity of adagrasib in patients with advanced solid tumors that have a KRAS G12C mutation, including NSCLC.
Dr. Riely reported data on 79 patients with advanced or metastatic NSCLC who had progressed despite being treated with chemotherapy and immunotherapy. Of these, 18 patients had participated in the phase 1/1b dose-escalation and dose-expansion phase of the study, and 61 had participated in the phase 2 portion. Adagrasib was given at a twice-daily dose of 600 mg.
The patients’ median age was 65 years, 85% were White, and 57% were women. Almost all (95%) were current or former smokers, which is unsurprising since the KRAS G12C mutation is rarely seen in never-smokers. Almost all patients had nonsquamous histology (96%) and had received PD-1 or PD-L1 inhibitors (92%).
Treatment-related adverse events of any grade occurred in 85% of patients, and 30% of patients had grade 3-4 events. The most frequent treatment-related grade 3-4 adverse events were fatigue (6%), increased ALT or AST (each 5%), QT prolongation (3%), anemia (2%), nausea (2%), and vomiting (2%).
Two grade 5 adverse events were recorded – a case of pneumonitis in a patient with recurrent pneumonitis and one case of cardiac failure. Adverse events led to discontinuation in 4.5% of patients.