The levels of MDR1 protein could be reconstituted in Cd44-negative osteosarcoma cells by re-introduction of the smallest isoform of CD44- the so-called standard isoform (CD44s), suggesting that this isoform was sufficient to confer doxorubicin resistance in osteosarcoma cells (Figure 2A,C). The gene discussed is ABCB1; the disease is osteosarcoma.