A small molecule inhibitor of polycomb complex protein BMI-1, a gene often overexpressed in tumors and therefore a popular therapeutic target in cancer. Anti-tumor effects of PTC 209 have been demonstrated in colorectal carcinoma, acute myeloid leukemia, multiple myeloma and head neck squamous cell carcinoma. As a regulator of self-renewal, inhibition of BMI-1 by PTC 209 also reduces growth of colorectal cancer initiating cells.