Combination with palbociclib and MTOR inhibitors is effective in patient samples in vitro and xenograft in vivo. (A-B) Viable primary ATLL cells were measured by the ³H-thymidine incorporation assay following treatment with palbociclib and everolimus (A) or AZD8055 (B) for 6 days. Count was normalized to DMSO-treated cells. (C-F) ATL43Tb(-) xenografts were treated with control, palbociclib (12.5 mg/kg body weight), everolimus (2.5 mg/kg body weight), or a combination of palbociclib and everolimus with same doses for 3 days per week for 3 weeks by intraperitoneal injection. (C) Representative IVIS imaging of the treated mice. (D) Quantification of tumor volumes obtained by bioluminescent signals using IVIS. (E) Tumor growth curves were obtained by caliper measurement in the tumor-bearing mice. (F) Normalized values of body weight of the treated mice. (G) Tumor growth curves measured by calipers in Su9T01 tumor-bearing mice. (H) Normalized body weight measurements of mice treated with indicated inhibitors in (G). Error bars represent the SEM of replicates (A-B,E-H). *P < .05, **P < .01, ***P < .001.