Aprepitant in Preventing Nausea and Vomiting in Patients Who Are Undergoing a Stem Cell Transplant

Inclusion: * 18 years of age or greater * must be scheduled for an autologous or allogeneic bone marrow or peripheral stem cell transplant * Eastern Cooperative Oncology Group(ECOG) performance status \< or = 2 * patients must have signed informed consent * must be able to swallow tablets and capsules * must be receiving a cyclophosphamide containing regimen. Exclusion: * patient has known sensitivity to aprepitant, ondansetron, or dexamethasone * patient has received another investigational drug in the past 30 days * patient has had emesis or requires antiemetic agents in the 48 hours prior to beginning conditioning therapy * patient has taken neurokinin-1 antagonists for 14 days prior to enrollment * patient is pregnant, has a positive serum human chorionic gonadotropin(hCg) or is lactating * patient has serum creatinine level \> or = 2\*ULN * patient has severe hepatic insufficiency (Child-Pugh score \>9) * patient drinks \> 5 drinks/day for the last year * patient with concurrent illness requiring systemic corticosteroid use other than planned dexamethasone during conditioning therapy