P681: EUROFLOW STANDARDIZATION TECHNIQUE AND NORMALIZATION PROCEDURES IN LONGITUDINAL FLOW CYTOMETRIC EXPRESSION ANALYSIS OF CD20 IN CLL PATIENTS RECEIVING ANTI-CD20 DIRECTED THERAPY. (23rd June 2022) - Walter, P. J.; Schilhabel, A.; Cramer, P.; von Tresckow, J.; Kohlscheen, S.; Fischer, K.; Eichhorst, B.; Böttcher, S.; Brüggemann, M.; Kneba, M.; Hallek, M.; Ritgen, M.