Inclusion Criteria:

• At least 18 years of age or at least the legal age of consent in the jurisdiction in which the study is taking place, whichever is the older age.
• Criterion amended per Amendment 1:
  • Diagnosis of SMM (per IMWG criteria) for ≤5 years with measurable disease at the time of randomization, defined as serum M protein ≥10 g/L or urine M protein ≥ 200 mg/24 hours or involved serum FLC ≥100 mg/L and abnormal serum FLC ratio.
• Criterion amended per Amendment 1:
  • Clonal BMPCs ≥10%; and
  • At least 1 of the following risk factors:
    • Serum M protein ≥30 g/L,
    • IgA SMM,
    • Immunoparesis with reduction of 2 uninvolved immunoglobulin isotypes (only IgA, IgM, and IgG should be considered in determination for immunoparesis; IgD and IgE are not considered in this assessment),
    • Serum involved: uninvolved FLC ratio ≥8 and <100, or
    • Clonal BMPCs >50% to <60% with measurable disease.
• ECOG performance status score of 0 or 1 (Attachment 1).
• Pretreatment clinical laboratory values meet the following criteria during the Screening Phase:
  • Absolute neutrophil count ≥1.0 x 109/L (ie, ≥1000/μL);
  • Platelet count ≥0 x 109/L (not permissible to transfuse a subject within 2 weeks prior to the Screening platelet count to reach this level);
  • Aspartate aminotransferase (AST) ≤2.5 x upper limit of normal (ULN);
  • Alanine aminotransferase (ALT) ≤2.5 x ULN;
  • Total bilirubin ≤2.0 x ULN, except in subjects with congenital bilirubinemia, such as Gilbert syndrome (in which case direct bilirubin ≤2.0 x ULN is required),
• Must sign an informed consent form (ICF) or their legally acceptable representative must sign indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study.
• Criterion amended per Amendment 1:
  • Contraceptive use by men or women should be consistent with local regulations regarding the use of contraceptive methods for subjects participating in clinical studies;
  • Women of childbearing potential must commit to either abstain continuously from heterosexual sexual intercourse or to use 1 method highly effective form of contraception (tubal ligation, intrauterine device, hormonal [birth control pills, injections, hormonal patches, vaginal rings or implants], or partner's vasectomy);
  • Contraception must begin 4 weeks prior to dosing. Highly effective contraception is indicated even where there has been a history of infertility, unless due to hysterectomy.
• A woman of childbearing potential must have a negative serum or urine pregnancy test at screening within 14 days prior to randomization. For requirements during the Treatment Phase.
• During the study and for 3 months after receiving the last dose of daratumumab, a woman must agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction.
• Willing and able to adhere to the prohibitions and restrictions specified in this protocol.

Exclusion Criteria:

• Multiple myeloma, requiring treatment, defined by any of the following:
  • Bone lesions (one or more osteolytic lesions on low-dose whole body computed tomography [LDCT], positron-emission tomography with computed tomography [PET-CT] or CT). Subjects who have benign/post-traumatic bone lesions visible on screening images as well as previous imaging, may be considered for inclusion. Details (diagnosis, location, duration) on benign/post-traumatic preexisting bone lesions that can be seen on the screening images (e.g., old fractures) and were also present on previous imaging are to be reported in the CRF;
  • Hypercalcemia (serum calcium >0.25 mmol/L [>1 mg/dL] higher than ULN or >2.75 mmol/L [>11 mg/dL]). Subjects who have clinically stable hypercalcemia attributable to a disease other than multiple myeloma (eg,  hyperparathyroidism) may be considered for inclusion after a case by case review by the medical monitor;
  • Renal insufficiency, preferably determined by creatinine clearance <40 mL/min measured or estimated using the MDRD (Attachment 2), or serum creatinine >177 μmol/L. Subjects who have clinically stable renal insufficiency attributable to a disease other than multiple myeloma (e.g., glomerulonephritis) may be considered for inclusion after a case by case review by the medical monitor;
  • Anemia, defined as hemoglobin <10 g/dL or >2 g/dL below lower limit of normal or both; transfusion support or concurrent treatment with erythropoietin stimulating agents is not permitted. Subjects who have clinically stable anemia attributable to a disease other than multiple myeloma (e.g., thalassemia, vitamin B12 deficiency, iron deficiency) may be considered for inclusion after a case by case review by the medical monitor (see Section 9.2.3).
  • Clonal BMPC percentage ≥60%;
  • Serum FLC ratio (involved:uninvolved) ≥100 (The involved FLC must be ≥100 mg/L);
  • More than 1 focal lesion ≥5 mm in diameter by MRI.
• Primary systemic AL (immunoglobulin light chain) amyloidosis.
• Criterion amended per Amendment 2:
• Exposure to any of the following:
  • Prior exposure to daratumumab or prior exposure to other anti-CD38 therapies;
  • Prior exposure to approved or investigational treatments for SMM or MM (including but not limited to conventional chemotherapies, IMiDs, or PIs). Stable standard dosing of bisphosphonate and denosumab as indicated for osteoporosis is acceptable;
  • Exposure to investigational drug (including investigational vaccines) or invasive investigational medical device for any indication within 4 weeks or 5 half-lives, whichever is longer, before Cycle 1, Day 1;
  • Ongoing treatment with corticosteroids with a dose >10 mg prednisone or equivalent per day at the time of randomization; or >280 mg cumulative prednisone dose or equivalent for any 4-week period in the year prior to randomization.
• Ongoing treatment with other monoclonal antibodies (e.g., infliximab, rituximab), immunomodulators (eg, abatacept, methotrexate, azathioprine, cyclosporine) or other treatments that are likely to interfere with the study procedures or results
• Received treatment (chemotherapy, surgery, etc.) for a malignancy (other than SMM) within 3 years before the date of randomization (exceptions are squamous and basal cell carcinomas of the skin, carcinoma in situ of the cervix or breast, or other non-invasive lesion), which is considered cured with minimal risk of recurrence within 3 years.
• Either of the following:
  • Known or suspected chronic obstructive pulmonary disease (COPD) with a forced expiratory volume in 1 second (FEV1) <50% of predicted normal;
  • Moderate or severe persistent asthma within the past 2 years, or currently has uncontrolled asthma of any classification. (Note that subjects who currently have controlled intermittent asthma or controlled mild persistent asthma are allowed in the study).  The LDCT/PET-CT/CT performed for screening should be taken into consideration to determine if additional pulmonary workup is required.
• Criterion amended per Amendment 1:
• Any of the following:
  • Known to be seropositive for human immunodeficiency virus (HIV);
  • Known to be seropositive for hepatitis B (defined by a positive test for hepatitis B surface antigen [HBsAg]). Subjects with resolved infection (e.g., subjects who are positive for antibodies to hepatitis B core antigen [antiHBc] and/or antibodies to hepatitis B surface antigen [antiHBs]) must be screened using real-time polymerase chain reaction (PCR) measurement of hepatitis B virus (HBV) DNA levels. Those who are PCR positive will be excluded;  EXCEPTION: Subjects with serologic findings suggestive of HBV vaccination (antiHBs positivity as the only serologic marker) AND a known history of prior HBV vaccination, do not need to be tested for HBV DNA by PCR.
  • Known to be seropositive for hepatitis C (except in the setting of a sustained virologic response [SVR], defined as aviremia at least 12 weeks after completion of antiviral therapy).
• Medical or psychiatric condition or disease (e.g., active systemic disease [including presence of auto-antibodies], uncontrolled diabetes) that is likely to interfere with the study procedures or results, or that in the opinion of the investigator, would constitute a hazard for participating in this study.
• Clinically significant cardiac disease, including:
  • myocardial infarction within 6 months with left ventricular dysfunction or uncontrolled ischemic cardiac disease before Cycle 1 Day 1, or unstable or uncontrolled disease/condition related to or affecting cardiac function (e.g., unstable angina, congestive heart failure, New York Heart Association Class III-IV);
  • Uncontrolled cardiac arrhythmia (Grade 2 or higher by National Cancer Institute-Common Terminology Criteria for Adverse Events [NCI-CTCAE] Version 4.03) or clinically significant ECG abnormalities;
  • Screening 12-lead ECG showing a baseline QT interval as corrected QT interval corrected for heart rate >470 msec.  The LDCT/PET-CT/CT performed for screening should be taken into consideration to determine if additional cardiac workup is required;
  • Criterion amended per Amendment 1:
    • Known allergies, hypersensitivity, or intolerance to corticosteroids, monoclonal antibodies, hyaluronidase, or other human proteins, or their excipients (refer to Daratumumab Investigator Brochure12), or known sensitivity to mammalian-derived products (including dairy allergy).
• Vaccination with live attenuated vaccines within 4 weeks of first study agent administration.
• Pregnant, breast-feeding, or planning to become pregnant while receiving study treatment or within 3 months after the last dose of daratumumab.
• Plans to father a child while receiving study treatment or within 3 months after the last dose of daratumumab.
• Major surgery (requiring general anesthesia or presence of other factors that determines surgery to be considered major) within 2 weeks before randomization or who have not fully recovered from surgery, or has surgery planned during the time the subject is expected to participate in the study or within 2 weeks after the last dose of daratumumab. Note: subjects with planned surgical procedures to be conducted under local anesthesia may participate. If there is a question whether a procedure is considered a major surgery, then the investigator must consult with the appropriate sponsor representative and resolve any issues before enrolling a subject in the study. 
• Known or suspected of not being able to comply with the study protocol (e.g., because of alcoholism, drug dependency, or psychological disorder). Subject has any condition for which, in the opinion of the investigator, participation would not be in the best interest of the subject (e.g., compromise the well-being) or that could prevent, limit, or confound the protocol-specified assessments. Subject is taking any prohibited medications.
  • NOTE: Investigators should ensure that all study enrollment criteria have been met at screening.
• If a subject's clinical status changes (including any available laboratory results or receipt of additional medical records) after screening but before the start of the Active Monitoring Phase (Arm A) or the first dose of daratumumab (Arm B) is given, such that he or she no longer meets all eligibility criteria, then the subject should be excluded from participation in the study.  Section 17.4, Source Documentation, describes the required documentation to support meeting the enrollment criteria. Subjects who fail to meet the inclusion and exclusion criteria (e.g., screen failures) may be rescreened if their condition changes. Rescreening must be discussed with and approved by the sponsor on a case-by-case basis. Subjects who are determined to be eligible for the study after rescreening must sign a new ICF and then will be assigned a new Subject number.