Evaluating the Efficacy and Safety of the Lower Dose of Bortezomib Plus Busulfan and Melphalan as a Conditioning Regimen in Patients With Multiple Myeloma Undergoing Autologous Peripheral Blood Stem Cell Transplantation- KMM103 Study

Inclusion Criteria:

* Patients with a confirmed diagnosis of multiple myeloma (MM)
* Symptomatic MM (multiple myeloma with related organ or tissue damage)
* The MM patients with induction chemotherapy with bortezomib-containing regimens (bortezomib±steroid±adrimycin)
* The MM patients who performed the peripheral blood stem cell collection and appropriate stem cell counts (CD34+ cells 2 x 106/kg).
* Age 20-65 years
* Performance status: ECOG (Eastern Cooperative Oncology Group) 0-2.
* Patient has measurable disease, defined as follows: measurable disease is defined as serum M-protein ≥ 1 g/dL or urine M-protein ≥ 200 mg/24 hours when the patients started the primary induction therapy.
* Cardiac ejection fraction ≥ 50 % as measured by MUGA or 2D ECHO without clinically significant abnormalities
* Adequate liver functions: - Transaminase (AST/ALT) \< 3 X upper normal value - Bilirubin \< 2 X upper normal value
* Adequate hematological function: Platelet count ≥ 75 x 109/L, hemoglobin ≥ 8 g/dL, (Prior RBC transfusion or recombinant human erythropoietin use is allowed), absolute neutrophil count (ANC) ≥ 1.0 x 109/L
* A negative serum or urine pregnancy test prior to treatment must be available both for pre menopausal women and for women who are \< 1 years after the onset of menopause.
* Expected survival 6 months
* Informed consent

Exclusion Criteria:

* Systemic AL amyloidosis, smoldering multiple myeloma or MGUS.
* Patient with plasma cell leukemia (\> 20% plasma cells in the PB and an absolute plasma cell count of at least 2000/μL)
* Patients who received an extensive radiation therapy within 4 weeks
* Patient is known to be Human Immunodeficiency Virus (HIV) positive.
* Patient has known clinically active Hepatitis B or C.
* Previous renal transplantation
* Severe peripheral neuropathy (Grade 2 or higher as defined by National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) Version 3.0)
* Any other malignancies within the past 5 years except curatively treated non-melanoma skin cancer or in situ carcinoma of cervix uteri
* Pregnant or lactating women, women of childbearing potential not employing adequate contraception
* Other serious illness or medical conditions i. Uncontrolled or severe cardiovascular disease, including myocardial infarction, within 6 months of enrollment, New York Heart Association (NYHA) Class III or IV heart failure, uncontrolled angina, clinically significant pericardial disease, or cardiac amyloidosis ii. History of significant neurological or psychiatric disorders including dementia or seizures iii. Active uncontrolled infection (viral, bacterial or fungal infection) iv. Active ulcers detected at gastroscopy v. Other serious medical illnesses
* Known hypersensitivity to any of the study drugs or its ingredients (i.e., hypersensitivity to compounds containing boron or mannitol)
* Concomitant administration of any other experimental drug under investigation, or concomitant chemotherapy, hormonal therapy, or immunotherapy.