FcγRIIb levels predict progression-free survival in MCL patients treated with rituximab regimens. (A) Immunohistochemistry for FcγRIIb in FL (top panel, flow cytometric quantification of FcγRIIb expression of corresponding viable cells shown and MCL bottom panel) samples. Representative examples of negative (left) and positive membranous (right) staining are shown. The top left panel demonstrates FcγRIIb staining in the normal mantle region, which serves as an internal positive control for the staining. (B) Progression-free survival of 16 MCL patients treated with rituximab-containing regimens classified on the basis of positive or negative FcγRIIb expression by immunohistochemistry (left, n = 8 per group, P < .05, log-rank test), and 12 MCL patients treated with frontline FCR or rituximab alone (right, n = 6 per group, P value not significant, log-rank test).