The pharmacokinetics (PK) and safety of single-dose alpelisib (300 mg) were assessed in participants with moderate to severe hepatic impairment (n = 6 each) compared with their matching healthy controls (n = 11). Blood samples were collected upto 144 hours post-dose and evaluated by liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay. The primary PK parameters (maximum plasma concentration [Cmax], area under the curve [AUC]infand AUClast) and secondary PK parameters (AUC0-t, apparent total body clearance [CL/F], apparent volume of distribution [Vz/F], time of maximum observed concentration [Tmax], and half-life [T1/2]) of oral alpelisib 300 mg were determined from individual plasma concentration-time profiles using non‑compartmental analysis. Cmaxof alpelisib decreased by approximately 17% in the moderate hepatic impairment group vs. the healthy control group (geometric mean ratio; GMR [90% confidence interval; CI], 0.833 [0.530, 1.31]). Cmaxin the severe hepatic impairment group was comparable to that of the healthy control group (GMR [90% CI], 1.00 [0.636, 1.58]). AUClastfor alpelisib decreased by approximately 27% in the moderate hepatic impairment group vs. the healthy control group (GMR [90% CI], 0.726 [0.487, 1.08]). AUClastwas 26% higher in the severe hepatic impairment group compared with the healthy control group (GMR [90% CI], 1.26 [0.845, 1.87]). Overall, 3 participants (13.0%) experienced at least 1 adverse event which were either grade 1 or 2. Adverse events did not lead to study drug discontinuation. No grade 3 or 4 adverse events, serious adverse events or deaths were reported. The results indicate that a single dose of alpelisib was well tolerated in this study population. There was no significant impact of moderate or severe hepatic impairment on the exposure of alpelisib.