In an open-label, phase 1/2, randomized clinical trial (VICTORIA) performed at 12 cancer centers in France, with good tolerability.
The study was published in JAMA Oncology.
Treatment of endometrial cancer involves a combination of surgery, radiation, and chemotherapy, but about 20% of patients relapse, usually within 5 years. HR+ endometrial cancer represents about 65% of endometrial cancers. It is usually endometrioid, and about 80% have phosphatase and tensin homologue (PTEN) mutations, while 36-52% have a mutation in the phosphoinositide 3-kinases/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway.
Endocrine therapy alone elicits a response rate of 15%-30% in HR+ endometrial cancer, generally in low-grade endometrioid subtypes. Most responses are short in duration. Aromatase inhibitors like anastrozole are used for more often than progestogens because they are better tolerated and they have a lower thromboembolic risk in this patient population. Previously, the phase 2 PARAGON trial showed a response rate of just 7% with anastrozole monotherapy, but 44% in women with recurrent HR+ endometrial cancer gained a clinical benefit.
Deregulation in the PI3K/AKT/mTOR pathway can also lead to hormone resistance, suggesting that combination of an mTOR inhibitor with endocrine therapy might have a synergistic effect.
mTOR inhibition alone or in combination with endocrine treatment has been investigated in some single-arm studies, with some encouraging progression-free survival results, but no clear objective response rate or overall survival benefit.
The new study included just 73 patients with a median age of 69.5 years: 49 received 125 mg vistusertib 2 days per week and 1 mg anastrozole daily and 24 received anastrozole only. The 8-week progression-free rate was 67.3% (unilateral 95% confidence interval, 54.7%) in the combination arm versus 39.1% (unilateral 95% CI, 22.2%) in the anastrozole-only arm.
Among 6 patients in the safety run-in period of the combination arm, there were no serious adverse events. Overall response rate was 24.5% (95% CI, 13.3-38.9%) in the combination arm and 17.4% (95% CI, 5.0-38.8%) in the anastrozole-only arm.
Over a median follow-up of 27.7 months, progression-free survival was 5.2 months in the combination arm (95% CI, 3.4-8.9 months) and 1.9 months (95% CI, 1.6-8.9) In the anastrozole-only arm. Common grade 2 or higher side effects linked to vistusertib included fatigue, lymphopenia, hyperglycemia, and diarrhea.
Although low tumor grade, endometrioid subtype, and HR+ status are associated with response to endocrine therapy, the low overall response and progression-free survival in the anastrozole arm suggest that better patient selection is needed. “The choice of treatment according to the histologic characteristics is not sufficient, and highly selected molecular criteria are necessary,” the authors wrote.
The study is limited by its small size and a lack of data on expression level of hormone receptors.
The study was funded by the National Cancer Institute of France.