Inclusion Criteria:

- Confirmed diagnosis of MRT or neuroblastoma, that has progressed despite standard
therapy or for which no effective standard therapy exists.

- Patients with CNS disease should be on stable doses of steroids for at least 7 days
prior to first dose of LEE011 with no plans for escalation.

- In expansion part, patients must have at least one measurable disease as defined by
RECIST v1.1.

- Patients must have a Lansky (≤ 16 years) or Karnofsky (> 16 years) score of at least
50.

Exclusion Criteria:

- Prior history of QTc prolongation or QTcF > 450 ms on screening ECG.

- Patients with the following laboratory values during screening:

- Serum creatinine > 1.5 x upper limit of normal (ULN) for age

- Total bilirubin >1.5 x ULN for age

- Alanine aminotransferase (ALT)/serum glutamic pyruvic transaminase (SGPT) > 3 x
ULN for age; aspartate aminotransferase (AST)/serum glutamic oxaloacetic
transaminase(SGOT) > 3 x ULN for age except in patients with tumor involvement
of the liver who must have AST/SGOT and ALT/SGPT ≤ 5 x ULN for age. For the
purpose of this study, the ULN for SGPT/ALT is 45 U/L.

- Patients who are currently receiving treatment with agents that are metabolized
predominantly through CYP3A4/5 and have a narrow therapeutic window and/or agents
that are known strong inducers or inhibitors CYP3A4/5 are prohibited. In particular,
enzyme-inducing antiepileptic drugs (EIAEDs).

- Other severe acute or chronic medical or psychiatric condition or laboratory
abnormality that may interfere with the interpretation of study results, and in the
judgment of the investigator would make the patient inappropriate for the study.