A large proportion (> 95%) of the 43 tumors analyzed in this study showed expression of CD74 (Fig. 4), compared to only 40% tumors with any detectable CD63 expression (17 out of 43), confirming previous reports of CD74 being expressed in breast cancer, but also indicating that the CD74/TIMP‐1 interaction may be the major TIMP‐1 associated signaling axis, at least in breast cancer. Here, CD63 is linked to breast carcinoma.