Measurement of SPF before treatment was significantly associated with clinical response , but sequential assessment of MDR phenotype identified three groups of tumors with distinct outcomes : ( 1 ) tumors with a positive and constant expression of MDR1 , in which prediction of resistance was restricted to patients treated by FAC ; ( 2 ) tumors without any detectable expression , in which resistance to FAC or FTC treatments was rarely observed ; and ( 3 ) tumors with an early ( Day 8 ) acquired or increased MDR1 gene expression , which were always resistant to therapy to both treatment regimens .
