MMP1 and breast carcinoma: The observation that MMP1 silencing is associated with increased primary tumor volume is novel and is in contrast to what has been observed in breast cancer where MMP1 silenced tumors demonstrated reduced primary tumor size.[39] The possible underlying mechanisms for increased primary tumor size in sarcoma is unclear and may be secondary to an underlying catabolism of anabolic factors or other mitogenic signaling molecules by MMP1.