Chemotherapy-induced nausea and vomiting (CINV) are among the most bothersome symptoms during cancer treatment according to children and their parents. Most children receiving highly emetogenic chemotherapy (HEC), including those receiving hematopoietic stem cell transplant (HSCT) conditioning, experience CIV despite receiving antiemetic prophylaxis. Olanzapine improves CINV control in adult cancer patients, has a track record of safe use in children with psychiatric illness, does not interact with chemotherapy and is inexpensive. We hypothesize that the addition of olanzapine to standard antiemetics will improve chemotherapy-induced vomiting (CIV) control in children receiving highly emetogenic chemotherapy

Planned receipt of HEC or cyclophosphamide ≥ 1 g/m2/day (≥ 33 mg/kg/day) for cancer treatment or autologous or allogeneic HSCT conditioning.81,82 Examples of HEC are: busulfan IV (myeloablative dosing), carboplatin ≥175mg/m²/dose, cisplatin ≥12mg/m²/dose, cytarabine ≥3g/m²/day, melphalan >140mg/m², methotrexate ≥12g/m²/dose and thiotepa ≥300mg/m²/dose.

Plan for inpatient admission from administration of first study drug dose until 24 hours following administration of last study drug dose.

Body weight of at least 12.5 kg

2.5 to < 18 years of age. Note that the minimum age requirement corresponds to an approximate body weight of 12.5 kg.

Samples for all laboratory tests will be obtained within one week prior to administration of the first chemotherapy dose of the study chemotherapy block or the first HSCT conditioning dose:

• Plasma creatinine within 1.5 times the upper limit of normal for age.
• Amylase within age-appropriate limits
• Plasma conjugated bilirubin within ≤ 3x upper limit of normal for age unless attributable to Gilbert's Syndrome
• ALT ≤ 5x upper limit of normal for age

Baseline ECG within the month prior to study drug administration without known clinically significant abnormalities including pathologic prolongation of QTc

A plan for scheduled, round-the-clock receipt of ondansetron, granisetron or palonosetron for antiemetic prophylaxis during administration of chemotherapy or HSCT conditioning.

Negative pregnancy test if female of childbearing potential

Patients of childbearing potential must consent to use adequate contraception (males and females) or agree to practice abstinence

Parent or child able to speak a language in which the (modified Pediatric Adverse Event Rating Scale (PAERS) is available.

Optional: Child participants in the optional assessment of nausea severity must be 4 to 18 years of age. Child and a parent/guardian must be English, Spanish or French-speaking. The Pediatric Nausea Assessment Tool58 (PeNAT) is validated in English-speaking children 4 to 18 years old with an English-speaking parent/guardian and has been translated into Spanish and French. The MAT is available in English, Spanish and French.