LMP2A/λ-MYC tumors are sensitive to CDK4/6 inhibitor abemaciclib treatment, whereas λ-MYC and LMP1/λ-MYC tumors are resistant. (A) 5-week-old pretumor mice of indicated phenotypes were treated with 1XPBS 0.5% methylcellulose as vehicle only (−) or 100 mg/kg per day abemaciclib (Abe) via oral gavage daily for 7 days and then sacrificed for the analysis at 6 weeks. Percentage masses of cervical lymph nodes were calculated for spleen and cervical lymph nodes. (B) Mice harboring tumors at ages of 8 to 40 weeks were treated with 1XPBS 0.5% methylcellulose only (−) or 100 mg/kg per day Abe daily for 7 days, and the percentage mass of spleen and total lymph node tumors developed in cervical, axillary, abdominal, and thoracic area were analyzed. Equivalent-age WT mice not treated with Abe were included as no tumor controls. (C) LMP2A/λ-MYC/Cks1^−/− mice harboring tumors at the ages of 10 to 25 weeks were treated with 1XPBS 0.5% methylcellulose only (−) or 100 mg/kg per day Abe daily for 7 days, and their percentage mass of spleen and total lymph node tumors were analyzed. Dot plot graphs represent the mean ± standard deviation. P values were calculated by unpaired t test, *P < .05, **P < .01, ***P < .001, and ****P < .0001.