While smcc-DM1, a non-cleavable linker-payload, is released upon degradation of antibodies by various proteases in the lysosome, the cleavable linker can be cleaved in the extracellular environment by secreted cathepsin B, suggesting that the MMAE of c12G1-vc-PAB-MMAE can be released into the extracellular environment before internalization into cancer cells, thereby reducing its therapeutic efficacy. This evidence concerns the gene CTSB and cancer.