Mutation sites in the ligand binding domain of PML-RARαafter relapse on protocol C9710 (ATRA/CT-arm). ▴ represents site of 17 missense mutations; and ▵, site of 2 deletion (Δ) mutations. Δ207-208, ΔK207Y208/T207 indicates deletion of lysine and tyrosine corresponding to amino acids 207 and 208 of normal RARα with maintenance of the normal downstream reading frame beginning with RARα threonine 209, now 207; similarly, Δ412-414, ΔE412M413L414/E415→E412.