BMI1 and head and neck squamous cell carcinoma: However, it has been shown that treatment with Cisplatin actually increases the CSC fraction in HNSCC tumors, and Cisplatin-resistant cells intrinsically express elevated levels of Bmi-1; there is also a direct association between Cisplatin dosage or resistance and Bmi-1 expression in vitro and in vivo (22, 95).