That VDD impairs RMCC and substitution improves RMCC strongly suggests that vitamin D substitution enhances rituximab efficacy , which must be confirmed in appropriately designed prospective trials addressing VDD and substitution not only in DLBCL , but also in malignancies treated with other antibodies , of which the major mechanism of action is antibody-dependent cellular cytotoxicity ( eg , trastuzumab in breast cancer and cetuximab in colorectal cancer ) .