CD44 in malignant disorders

CD44 has been implicated to act in processes such as lymphocyte homing, haematopoiesis, tumor dissemination, lymphocyte activation, pattern formation in embryogenesis and inflammatory reactions. Possible explanations for the supposedly multipurpose nature of CD44 are the existence of an enormous number of isoforms and/or the potential likelihood that the role of CD44 in all these diverse processes is not so manifold as it sounds, because we still vastly lack understanding of the function of the variant isoforms. The purpose of this review article is not to repeat the details of the many review articles and commentaries which appeared recently on CD44 (Haynes et al., 1991a; Underhill, 1992; Gallagher, 1992; Günthert, 1993; Lesley et al., 1993; Kincade, 1993; Kincade et al., 1993; Herrlich et al., 1993a and b; Koopman et al., 1993a; East and Hart, 1993; Pals et al., 1993a and b; Zöller and Kaufmann, 1994; Sherman et al., 1994; Tanabe and Saya, 1994; Tarin and Matsumura, 1994; Isacke, 1994; Ponta et al., 1994; Moll et al., 1994; Lazaar and Puré, 1995; Günthert et al., 1995; Ruiz et al., 1995; Stauder and Günthert, 1995; Cooper and Dougherty, 1995; Zöller, 1995; Ponta et al., 1995; Sleeman et al., 1995; including those from the current series: Sherman et al., 1996; Zöller et al., 1996; Sy et al., 1996; Ristamäki et al., 1996), but to try to focus on additional aspects. Do the recent studies on correlation between CD44 and tumor progression or inflammation provide evidence for a functional involvement of CD44 in these processes? How does CD44 fit into the current view of the network of metastasis related molecules (cf articles in the present CTMI series and Ruiz and Günthert, 1995)?