Inclusion Criteria:

1. Age 18 to 75 years, inclusive.

2. Study participants must have a diagnosis of multiple myeloma and are eligible for the
planned ASCT.

3. Untreated bone marrow sample was shipped to Princess Margaret Hospital for MRD assay.

4. Must have been treated with a velcade-based induction regimen. No limit to the number
of cycles of induction.

5. Study participants in whom the minimum stem cell dose of 2.0 x 106 cluster of
differentiation (CD)34+ cells/kg has been collected.

6. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0-2.

7. Negative beta-human chorionic gonadotropin (β-HCG) pregnancy test in all women of
child-bearing potential (WOCBP).

8. Ability to provide written informed consent prior to initiation of any study-related
procedures, and ability, in the opinion of the Principal Investigator, to comply with
all requirements of the study.

Exclusion Criteria:

1. Myeloma progression at any time since starting initial therapy for myeloma.

2. Prior treatment history of ASCT for any medical reason.

3. Prior treatment history of high-dose chemotherapy with stem cell rescue for any
medical reason, not limited to myeloma treatment.

4. Prior treatment with busulfan or gemtuzumab ozogamicin for any reason.

5. Systemic amyloidosis.

6. Left ventricular ejection fraction (LVEF) < 45% as measured by either multi-gated
acquisition scan (MUGA) or echocardiogram (ECHO) performed within 75 days prior to
day of busulfan dose. If cyclophosphamide was used for stem cell harvest, an ECHO or
MUGA must be done after the stem cell collection and prior to enrollment to confirm
adequate cardiac function.

7. Uncontrolled arrhythmia or symptomatic cardiac disease at the time of screening.

8. Symptomatic pulmonary disease, based on Forced Expiratory Volume in 1 Second (FEV1),
Forced Vital Capacity (FVC) or Diffusing Capacity of the Lung for Carbon Monoxide
(DLCO) < 50% of predicted (corrected for hemoglobin) measured within 75 days prior to
day of busulfan dose.

9. Aspartate transaminase (AST)/alanine transaminase (ALT) ≥ 3 x the upper limit of
normal (ULN).

10. History of elevated total serum bilirubin >2 mg/dL that had been caused by previous
chemotherapy at any point, or total bilirubin > 2.0 mg/dL at the time of screening
with the exception of Gilbert's disease.

11. Hepatic synthetic dysfunction evidenced by prolongation of the prothrombin time as
International Normalized Ratio (INR) ≥ 2.0 at the time of screening.

12. Any previous history of fulminant liver failure, cirrhosis, alcoholic hepatitis,
esophageal varices, hepatic encephalopathy, ascites related to portal hypertension,
bacterial or fungal liver abscess, biliary obstruction, and symptomatic biliary
disease.

13. Prior total body irradiation therapy, or radiation therapy directly applied to the
liver.

14. Patients with a known history of hepatitis B or hepatitis C should be on appropriate
anti-viral therapy. Even so, these cases must be discussed with the sponsor and
approval obtained prior to screening.

15. Known history of or current HIV infection, or active hepatitis B or c infection or
any uncontrolled active infection of any kind at the time busulfan administration.

16. Serum creatinine >177 umol/L at the time of screening.

17. Women who are pregnant or lactating.

18. Current or history of drug and/or alcohol abuse.

19. Use of other investigational therapies within 30 days of enrollment in this study.

20. Clinically significant abnormality in medical history or upon examination that might
interfere with the outcomes of the study in the opinion of the investigator.

21. Any patient, who in the opinion of the investigator, should not participate in this
study.