Tumor infiltrating neutrophils release gelatinase B/MMP-9 in TIMP-free form, facilitating tumor-associated differential gelatinase B/MMP-9 and TIMP-1 expression [168,169] Furthermore, the differential up-regulation of gelatinase B/MMP-9 but not TIMP-1 expression has been reported in human ovarian cancer [170], skin cancer [171], squamous cell carcinoma of the hypopharynx [172] and colon and rectal tumours in vivo [173], and has also been demonstrated in malignant melanomas induced in metallothionin/RET transgenic mice [174]. Here, MMP9 is linked to hypopharynx squamous cell carcinoma.