EPO does not relieve tipifarnib BFU-E growth inhibition. (A) BFU-E colony number in patients with PV (n = 8) at 1.5 μM tipifarnib concentration in the absence or presence of EPO. □ indicates control; ▦, EPO; ▨, tipifarnib; and ▪, EPO + tipifarnib. Pt indicates patient number. (B) indicates dose-dependent BFU-E growth inhibition: ratio of BFU-E colony growth assessed in PV samples between medium alone and tipifarnib-treated samples (n = 8). ▪ indicates EPO rescue of tipifarnib BFU-E growth inhibition: ratio of BFU-E colony growth between EPO- and tipifarnib + EPO–treated samples (n = 8). BFU-E colonies were counted at day 14 with each experiment assessed in triplicate. Error bars indicate 95% confidence intervals.