Experimental combo offers hope for Tough-to-Treat leukemias

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Participants with a diagnosis of histologically confirmed relapsed or refractory (R/R) acute myeloid leukemia or R/R acute lymphoblastic leukemia for which no available standard therapies are indicated or anticipated to result in a durable response. 2. Only participants with R/R ALL will be eligible for cohort C 3. Age \>/= 15 years. 4. Participants must not have had leukemia therapy for 14 days prior to starting palbociclib. However, participants with rapidly proliferative disease may receive hydroxyurea as needed until 24 hours prior to starting therapy on this protocol and starting the first cycle of study. 5. Adequate organ function as defined below: * liver function (bilirubin \< 2mg/dL, AST and/or ALT \<3 x ULN - or \<5 x ULN if related to leukemic involvement) * kidney function (creatinine \< 1.5 x ULN ). * known cardiac ejection fraction of \> or = 45% within the past 3 months 6. ECOG performance status of ≤ 2. 7. A negative urine pregnancy test is required within 1 week for all women of childbearing potential prior to enrolling on this trial. 8. Participants must have the ability to understand the requirements of the study and signed informed consent. A signed informed consent by the participants or his legally authorized representative is required prior to their enrollment on the protocol. Exclusion Criteria: 1. Participants women are excluded from this study because the agent used in this study has the potential for teratogenic or abortifacient effects. Because there is a potential risk for adverse events in nursing infants secondary to treatment of the mother with the chemotherapy agents, breastfeeding should also be avoided. 2. Uncontrolled intercurrent illness including, but not limited to active uncontrolled infection, symptomatic congestive heart failure (NYHA Class III or IV), unstable angina pectoris, clinically significant cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. 3. Participant with documented hypersensitivity to any of the components of the therapy program. 4. Participants with active, uncontrolled CNS leukemia will not be eligible. 5. Men and women of childbearing potential who do not practice contraception. Women of childbearing potential and men must agree to use contraception prior to study entry and for the duration of study participation. 6. Participants with known history of serous retinopathy will not be eligible. 7. Prior treatment with palbociclib,