CD6, a novel cell surface marker for prostate cancer progression?

Abstract

CD6 is involved in cell–cell interactions via binding with CD166. Over‐expression of CD166 is a marker for disease progression in prostate, colon, and breast cancer, whereas the expression of CD6 by epithelial tumor cells has not yet been described.We studied CD6 and CD166 expression, by immunohistochemistry, in 14 prostate primary tumors of Gleason Scores (GS) 6 to 9, 3 metastatic lymph nodes (LNs), and, by flow cytometry in 2 prostate cancer cell lines (PC3 and DU145).We show that prostate tumor cells express CD166, with a stronger expression in high GS. 6/9 specimens of GS 6 and 7 did not show any tumor cells expressing CD6. Few CD166+CD6+ cells were respectively detected in 1/3 and 1/6 specimens of GS 6 and 7. In contrast, large areas with numerous CD166+CD6+ tumor cells were detected in all (5/5) specimens of GS 8 and 9, and 1/6 GS7. Infiltration by CD6 expressing tumor cells was detected in all 3 invaded LNs. CD6 was strongly expressed by 15% of the PC3 and DU145 cells, while most of these cells weakly expressed CD6, and a few were CD6‐. Interestingly all MUC‐1 positive PC3 cells strongly expressed CD6.Our study shows for the first time CD6 expression in prostate cancer, in high GS specimens and LNs, and suggests that CD6/CD166 might be involved in cancer progression. Further studies are necessary to assess the functional phenotype of tumor cells subsets depending on CD6 and CD166 expression.