CD44 and cancer: These reports have shown that CD200 is co-expressed with cancer stem cell markers in prostate (CD44), breast (CD44 + CD24-), and colon (CD133) cancer cells, as well as in glioblastoma (CD133) cells [17]; furthermore, CD200-expressing human basal cell carcinoma cells were shown to initiate tumor growth [18] and were resistant to etoposide [19].