Results
A total of 21 patients were enrolled on Stratum I and 14 patients on Stratum II. The MTD for both strata was 75 mg/m2. Palbociclib absorption (mean Tmax between 4.9 and 6.6 h) and elimination (mean half-life between 11.3 and 19.5 h) were assessed. The most common toxicity was myelosuppression. Higher palbociclib exposure was associated with grade 3/4 neutropenia and leukopenia. No patients had an objective response to palbociclib therapy.