Decitabine has cytotoxic activity in ATLL. Results from cell-viability assays following 5 days of decitabine treatment in Japanese (A) and North American (B) ATLL samples. (C) Summary of decitabine IC₅₀ doses for all samples tested with EP300 and TP53 mutation status. (D-E) Doxorubicin and decitabine combination showed synergistic efficacy in 1 ATLL cell line and 1 North American ATLL culture. (F) Apoptosis measured by Annexin V/propidium iodide staining in decitabine-treated samples. Results shown are representative of 2 (ATL43Tb⁻) and 3 (ATL18) independent experiments. (G) Reduction in total 5-methylcytosine content after 48 hours of decitabine treatment at 0.6 μM was quantified by mass spectrometry. *P < .05. (H) Volcano plot. RNA-seq analysis revealed many re-expressed genes in 4 primary samples (ATL18, ATL21, ATL29, ATL30) following decitabine treatment.