Strikingly, the co-cultures of PyMT breast cancer cells expressing CTSB and CTSZ and Mɸ being double deficient for these proteases revealed a reduction of those enzymes to levels of 7.97% (CTSB, FC log2(KO/wt)-3.65) and 19.3% (FC log2(KO/wt)-2.37) compared to co-cultures in which cancer cells and Mɸ were wild type for both CTSB and CTSZ. This evidence concerns the gene CTSB and cancer.