Established from the peripheral blood of a 24-year-old man with refractory acute promyelocytic leukemia after mediastinal granulocytic sarcoma; however, PL-21 cells do not carry the t(15;17); based on morphology, surface marker expression of CD14/CD68 and expression of the monocyte-specific esterase, PL-21 cells appear to be rather of monocytic origin; we found that PL-21 carries an FLT3 internal tandem duplication
