Taselisib is the first agent in its class to specifically block the PI3K alpha isoform that is found to be mutated in approximately 40% of advanced ER-positive breast cancer. The agent has been shown to offer clinical benefits in early trials for patients with head and neck and some gynecologic cancers.
In the phase 3 SANDPIPER trial, 516 women with locally advanced or metastatic ER-positive, HER2-negative breast cancer that had progressed or recurred following aromatase inhibitor therapy were enrolled and randomly assigned on a 2:1 basis to receive fulvestrant plus taselisib (340 patients) or fulvestrant plus a placebo (176 patients).
As noted, the median progression-free survival was 7.4 months for women who received the combination, compared with 5.4 months for controls. The stratified hazard ratio was 0.70 favoring taselisib (P = .0037).
But also as noted, the addition of taselisib “clearly led to toxicity,” Dr. Baselga said.