Morphology of NB4 (A, B, and C) and NB4/As (D, E, and F) cell lines on RA or the combination of RA and As₂O₃ treatment. (A and D) Before treatment. (B and E) After 1 day of treatment with 1 μmol/L As₂O₃. (C) After 1 day of treatment with 1 μmol/L all-trans RA and 1 μmol/L As₂O₃. (F) After 4 days of treatment with 1 μmol/L RA and 1 μmol/L As₂O₃.