ABCB1 and in situ carcinoma: TUBB3 siRNA reduced the TUBB3 mRNA level by 47% and the ABCB1 mRNA level by 19% in A549-PacR/5-FU-induced subcutaneous tumors whereas in PC-3-PacR/CIS tumors, TUBB3 was reduced by 31% and ABCB1 by 29% relative to the mRNA levels from tumors induced by scramble siRNA transfected cells (Figure 6L).