Background Cyclin D has been shown to play an essential role in acute lymphoblastic leukemia (ALL) initiation and progression, providing rationale for targeting the CDK4/6-cyclin D complex that regulates cell cycle progression. Procedure The Children’s Oncology Group AINV18P1 phase 1 trial evaluated the CDK4/6 inhibitor, palbociclib, in combination with standard four-drug reinduction chemotherapy in children and young adults with relapsed/refractory B- and T-cell lymphoblastic leukemia (ALL) and lymphoma. Palbociclib (50 mg/m 2/dose) was administered orally once daily for 21 consecutive days, first as a single agent (days 1-3) and subsequently combined with reinduction chemotherapy. This two-part study was designed to determine the maximum tolerated dose (MTD) or recommended phase 2 dose (RP2D) followed by an expansion pharmacokinetic (PK) cohort. Results Twelve heavily pretreated patients enrolled, all of whom were evaluable for toxicity. One dose-limiting hematologic toxicity (DLT) occurred at the starting dose of 50 mg/m 2/dose orally for 21 days. No additional DLTs were observed in the dose determination or PK expansion cohorts and overall rates of grade 3/4 non-hematologic toxicities were comparable to those observed with the chemotherapy platform alone. Five complete responses were observed, two among four patients with T-ALL and three among seven patients with B-ALL. Pharmacokinetic studies showed similar profiles with both liquid and capsule formulations of palbociclib. Conclusions Palbociclib in combination with reinduction chemotherapy was well tolerated with a RP2D of 50 mg/m 2/day for 21 days. Complete responses were observed among heavily pretreated patients.

Background: Pediatric brain tumor survivors are at risk for poor social outcomes. It remains unknown whether cognitive sparing with proton radiotherapy (PRT) supports better social outcomes relative to photon radiotherapy (XRT). We hypothesized that survivors treated with PRT would outperform those treated with XRT on measures of cognitive and social outcomes. Further, we hypothesized that cognitive performance would predict survivor social outcomes. Procedure: Survivors who underwent PRT (n=38) or XRT (n=20) participated in a neurocognitive evaluation >1 year post-radiotherapy. Group differences in cognitive and social functioning were assessed using ANCOVA. Regression analyses examined predictors of peer relations and social skills. Results: Age at evaluation, radiation dose, tumor diameter, and sex did not differ between groups (all p>0.05). However, XRT participants were younger at diagnosis (XRT M=5.0 years, PRT M=7.6 years) and further out from radiotherapy (XRT M=8.7 years, PRT M=4.6 years). The XRT group performed worse than the PRT group on measures of processing speed (p=0.01) and verbal memory (p<0.01); however, social outcomes did not differ by radiation type. The proportion of survivors with impairment in peer relations and social skills exceeded expectation (2(1)=38.67, p<0.001; 2(1)=5.63, p<0.05), and verbal memory approached significance as a unique predictor of peer relations (t=-2.01, p=0.05). Total tumor RT dose significantly predicted social skills (t=-2.23, p<0.05). Conclusions: Regardless of radiation modality, survivors are at risk for social challenges, with one-quarter being socially excluded or undervalued. Deficits in verbal memory may place survivors at particular risk. Results support monitoring of cognitive and social functioning throughout survivorship.