Abstract Biomarkers are used as tools in cancer diagnostics
and in treatment stratification. In most cancers, there are
increased levels of one or several members of the matrix
metalloproteinases (MMPs). This is a family of proteolytic
enzymes that are involved in many phases of cancer progres-
sion, including angiogenesis, invasiveness, and metastasis. It
has therefore been expected that MMPs could serve as both
diagnostic and prognostic markers in cancer patients, but
despite a huge number of studies, it has been difficult to
establish MMPs as cancer biomarkers. In the present paper,
we assess some of the challenges associated with MMP re-
search as well as putative reasons for the conflicting data on
the value of these enzymes as diagnostic and prognostic
markers in cancer patients. We also review the prognostic
value of a number of MMPs in patients with lung, colorectal,
breast, and prostate cancers. The review also discusses MMPs
as potential target molecules for therapeutic agents and new
strategies for development of such drugs.