To characterise the phenotype associated with wild-type and variant CYP1B1 genotypes, we selected two HNSCC cell lines, CAL27 and CAL33, which do not express CYP1B1 at a detectable level as estimated by Western blot (Supplementary Fig. 1A, upper panel). Here, CYP1B1 is linked to head and neck squamous cell carcinoma.