CD9 is a crucial regulator of cell adhesion in the immune system and plays important physiological roles in hematopoiesis, blood coagulation or viral and bacterial infections. It is involved in the transendothelial migration of leukocytes which might also be hijacked by cancer cells during their invasion and metastasis. CD9 is found at the cell surface and the membrane of exosomes affecting cancer progression and therapy resistance. High expression of CD9 is mostly associated with good patients outcome, with a few exceptions. Discordant findings have been reported for breast, ovarian, melanoma, pancreatic and esophageal cancer, which might be related to using different antibodies or inherent cancer heterogeneity. According to in vitro and in vivo studies, tetraspanin CD9 is not clearly associated with either tumor suppression or promotion. Further mechanistic experiments will elucidate the role of CD9 in particular cancer types and specific conditions.

Department of Clinical and Molecular Pathology Institute of Molecular and Translational Medicine Faculty of Medicine and Dentistry Palacky University Olomouc Czechia

Department of Clinical and Molecular Pathology University Hospital Olomouc Olomouc Czechia

Department of Cytokinetics Institute of Biophysics of the Czech Academy of Sciences Brno Czechia

Department of Experimental Biology Faculty of Science Masaryk University Brno Czechia

Department of Pathology EUC Laboratore CGB a s Ostrava Czechia

International Clinical Research Center St Anne's University Hospital Brno Czechia

National Centre for Biomolecular Research Faculty of Science Masaryk University Brno Czechia

Proteomics Core Facility Central European Institute of Technology Masaryk University Brno Czechia

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