Methods
Palbociclib was administered orally starting at 50 mg/m2 daily for the first 21 days of a 28 day course. Dose escalation was according to the Rolling-6 statistical design in less heavily (Stratum I) and heavily pretreated (Stratum II) patients, and MTD was determined separately for each group. Pharmacokinetic studies were performed during the first course, and pharmacodynamic studies were conducted to evaluate relationships between drug levels and toxicities. Pharmacogenetic analyses were based on pre-treatment samples.