A Study to Learn About the Study Medicine (Elranatamab) in Participants With Multiple Myeloma That Has Come Back After Responding to Treatment or Has Not Responded to Treatment

Number of Participants With Dose Limiting Toxicities (DLTs): Part 2A

Hematological: grade 4 neutropenia lasting \>5 days; febrile neutropenia; grade \>=3 neutropenia with infection; grade 4 thrombocytopenia; grade 3 thrombocytopenia with grade \>=2 bleeding. Non-hematological: grade \>=4 adverse events (AEs); grade 3 CRS (except CRS events: not been maximally treated or improved to grade \<=1 within 48 hours); grade 3 AEs (except: AEs attributed to a CRS event; grade 3 nausea, vomiting and diarrhea that improve to grade \<= 2 within 72 hours after maximal medical management has been initiated, grade 3 fatigue lasting \<1 week; grade 3 AEs that recover to baseline or grade 1 within 5 days); confirmed drug-induced liver injury meeting Hy's law criteria; grade 3-4 laboratory abnormalities; other clinically important or persistent AEs; Grade 3 injection site reaction. CTCAE version 5.0: Grade 1: Mild AE, Grade 2: Moderate, Grade 3: severe, and grade 4: life-threatening consequences; urgent intervention indicated. Grade 5: death related to AE.

Time frame: Part 2A: 28 days starting from the first 116 or 152 mg dose

Number of Participants With Adverse Events (AEs) and Serious AEs (SAEs) [All Causalities and Treatment Related]: Parts 1 and 2

An AE is any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An SAE is defined as any untoward medical occurrence that, at any dose, meets 1 or more of the criteria listed below: Results in death, requires inpatient hospitalization or prolongation of existing hospitalization, life-threatening, congenital anomaly/birth defect etc. A treatment-related AE was any untoward medical occurrence attributed to the study drug in a participant who received study drug. Relatedness to study drug was assessed by the investigator.

Time frame: Day 1 of dosing up to 90 days post last dose (maximum treatment duration 25 cycles, follow up to 790 days)

Number of Participants With Maximum Grade 3 or 4 and Grade 5 AEs [All Causalities and Treatment Related] Per National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) v5: Parts 1 and 2

An AE was any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. A treatment-related AE was any untoward medical occurrence attributed to the study drug in a participant who received study drug. Relatedness to study drug was assessed by the investigator. AEs were graded according to NCI CTCAE version 5.0 as Grade 1 indicates Mild AE, Grade 2 indicates Moderate AE, Grade 3 indicates severe AE, and grade 4 indicates life-threatening consequences; urgent intervention indicated. Grade 5 indicates death related to AE.

Time frame: Day 1 of dosing up to 90 days post last dose (maximum treatment duration 25 cycles, follow up to 790 days)

Number of Participants With Adverse Events of Special Interest (AESI)- CRS and Immune Effector Cell-associated Neurotoxicity Syndrome (ICANS) [All Causalities and Treatment Related]: Parts 1 and 2

CRS and ICANS were assessed according to ASTCT criteria. ASTCT for ICANS: Grade 1 \[immune effector cell-associated encephalopathy (ICE, overall score range 0-10, higher score = better condition) score 7-9, awakens spontaneously\]; Grade 2 \[ICE score 3-6, awakens to voice\]; Grade 3 \[ICE score 0-2, awakens only to tactile stimulus, any clinical seizure that resolves rapidly or non-convulsive seizures on EEG that resolve with intervention, focal/local oedema on neuroimaging\]; Grade 4 \[ICE 0 (unarousable and unable to perform ICE), Unarousable or requires vigorous or repetitive tactile stimuli to arouse. Stupor or coma, Life-threatening prolonged seizure (\>5 min); or repetitive clinical or electrical seizures without return to baseline in between, deep focal motor weakness such as hemiparesis or paraparesis, Diffuse cerebral oedema on neuroimaging; decerebrate or decorticate posturing; or cranial nerve VI (abducens nerve) palsy; or papilledema; or Cushing's triad\].

Time frame: Day 1 of dosing up to 90 days post last dose (maximum treatment duration 25 cycles, follow up to 790 days)

Number of Participants With Hematological Measures With Baseline CTCAE Grade >=2 Shifted to a Maximum CTCAE Grade 3-4: Parts 1 and 2

Hematology results were graded according to the NCI CTCAE version 5.0 for relevant parameters, Grade 1 indicates Mild AE, Grade 2 indicates Moderate AE, Grade 3 indicates severe AE, and grade 4 indicates life-threatening consequences; urgent intervention indicated, Grade 5 indicates death related to AE. Hematological measures included Hemoglobin, Platelet count, WBC count, Plasma cell count. Absolute: Neutrophils, Eosinophils, Monocytes, Basophils, Lymphocytes, Plasma cells etc.

Time frame: Parts 1 and 2: From start of treatment to end of the study (approximately 3 years 7 months)

Number of Participants With Clinical Chemistry Parameters With Baseline CTCAE Grade >=2 Shifted to a Maximum CTCAE Grade 3-4: Parts 1 and 2

Clinical chemistry data included BUN (Blood urea nitrogen), Creatinine, Glucose (non-fasting), Total Calcium, Sodium, Potassium, Chloride, Magnesium, Phosphorus or Phosphates, Aspartate aminotransferase (AST), Alanine aminotransferase (ALT), Total bilirubin, Alkaline phosphatase, Albumin, Chloride, Total CO2 (bicarbonate), Total protein, Lactate dehydrogenase (LDH), Uric acid, Serum beta-2 microglobulin.

Time frame: Parts 1 and 2: From start of treatment to end of the study (approximately 3 years 7 months)

Number of Participants With Liver Function Tests Abnormalities: Parts 1 and 2

Alanine aminotransferase, aspartate aminotransferase, Alkaline Phosphatase, and total bilirubin (TBILI) were used to assess possible drug induced liver toxicity.

Time frame: Parts 1 and 2: From start of treatment to end of the study (approximately 3 years 7 months)

Objective Response Rate (ORR) Per International Myeloma Working Group (IMWG) Response Criteria as Determined by Investigator: Parts 1 and 2

ORR: % of participants with objective response. stringent complete response (sCR):CR; ii) normal serum free light chain (FLC) ratio; absence of clonal cells in bone marrow biopsy (BMB)/ bone marrow aspirate (BMA) by immunohistochemistry or immunofluorescence. CR: negative immunofixation on serum and urine, disappearance of any soft tissue plasmacytomas and \<5% plasma cells in BMA. If the only measurable disease is by serum FLC levels, CR was normal serum FLC ratio of 0.26-1.65. VGPR:Serum and urine M-protein detectable by immunofixation but not on electrophoresis;\>=90% reduction in serum M-protein plus urine M-protein level \<100 mg/24 h; if only measurable disease is by serum FLC levels, VGPR:\>=90% decrease in difference between involved and uninvolved serum FLC levels; in addition if present at baseline, \>90% reduction compared to baseline in size of soft tissue plasmacytomas. PR:≥50% reduction of serum M-protein and reduction in 24 hours urinary M-protein by ≥90% or to \<200 mg/24 h.

Time frame: Parts 1 and 2: From start of treatment to end of the study (approximately 3 years 7 months)

Complete Response Rate (CRR) Per IMWG Response Criteria as Determined by Investigator: Parts 1 and 2

CRR was defined as the percentage of participants with a BOR of confirmed sCR/CR per IMWG response criteria as determined by investigator. sCR: i) CR; ii) normal serum FLC ratio and absence of clonal cells in BMB/BMA by immunohistochemistry or immunofluorescence (κ/λ ratio \<=4:1 or \>=1:2 for κ and λ participants, respectively, after counting \>=100 plasma cells; iii) if the only measurable disease was by serum FLC levels, sCR was defined as normal serum FLC ratio of 0.26 to 1.65 plus absence of clonal cells in BMB/BMA b by immunohistochemistry or immunofluorescence (κ/λ ratio \<=4:1 or \>=1:2 for κ and λ participants, respectively, after counting \>=100 plasma cells). CR: i) negative immunofixation on serum and urine, disappearance of any soft tissue plasmacytomas and \<5% plasma cells in BMA; ii) if the only measurable disease was by serum FLC levels, CR was defined as normal serum FLC ratio of 0.26 to 1.65 plus criteria (i).

Time frame: Parts 1 and 2: From start of treatment to end of the study (approximately 3 years 7 months)

Time to Response (TTR) Per IMWG Response Criteria as Determined by Investigator: Parts 1 and 2

Time to response was defined for participants with an objective response per IMWG criteria, as the time from the date of first dose to the first documentation of objective response that was subsequently confirmed.

Time frame: Parts 1 and 2: From start of treatment to end of the study (approximately 3 years 7 months)

Duration of Response (DOR) Per IMWG Response Criteria as Determined by Investigator: Parts 1 and 2

DOR: time from the first documentation of objective response, until confirmed PD, or death due to any cause, whichever occurred first. PD: Increase of \>=25% from lowest confirmed response value in any 1 or more of following: serum M-component (absolute increase must be \>=0.5 g/dL); serum M-protein increase \>=1 g/dL, if lowest M component was \>=5 g/dL; urine M-protein (absolute increase must be \>=200 mg/24 h). In participants without measurable serum and urine M-protein levels, difference between involved and uninvolved serum FLC levels (absolute increase must be \>10 mg/dL). In participants without measurable serum, urine M-protein levels and involved serum FLC levels, BM plasma-cell % irrespective of baseline status (must be \>=10%). Appearance of a new lesion, \>=50% increase from nadir in SPD of \>1 lesion, or \>=50% increase in longest diameter of a previous lesion \>1 cm in short axis. \>=50% increase in circulating plasma cells (minimum of 200 cells per mcL) if only measure of disease.

Time frame: Parts 1 and 2: From start of treatment to end of the study (approximately 3 years 7 months)

Duration of Complete Response Rate (DOCR) Per IMWG Response Criteria as Determined by Investigator: Parts 1 and 2

DOCR was defined as the time from the first documentation of sCR or CR that was subsequently confirmed, until confirmed PD per IMWG criteria, or death due to any cause, whichever occurred first. sCR: i) CR; ii) normal serum FLC ratio and absence of clonal cells in BMB/BMA by immunohistochemistry or immunofluorescence (κ/λ ratio \<=4:1 or \>=1:2 for κ and λ participants, respectively, after counting \>=100 plasma cells; iii) if the only measurable disease was by serum FLC levels, sCR was defined as normal serum FLC ratio of 0.26 to 1.65 plus absence of clonal cells in BMB/BMA b by immunohistochemistry or immunofluorescence (κ/λ ratio \<=4:1 or \>=1:2 for κ and λ participants, respectively, after counting \>=100 plasma cells). CR: i) negative immunofixation on serum and urine, disappearance of any soft tissue plasmacytomas and \<5% plasma cells in BMA; ii) if the only measurable disease was by serum FLC levels, CR was defined as normal serum FLC ratio of 0.26 to 1.65 plus criteria (i).

Time frame: Parts 1 and 2: From start of treatment to end of the study (approximately 3 years 7 months)

Progression Free Survival (PFS) Per IMWG Response Criteria as Determined by Investigator: Parts 1 and 2

PFS was defined as the time from the date of first dose until confirmed PD per IMWG criteria, or death due to any cause, whichever occurred first. Analysis was performed using Kaplan-Meier method. Participants with no PD event or death or who started a new anticancer therapy prior to an event or with an event after a gap of 2 or more missing disease assessments were censored on the date of last adequate disease assessment. Participants who did not have an adequate post-baseline disease assessment were censored on the date of first dose of study intervention unless death occurred on or before the time of the second planned disease assessment (\<=8 weeks after the date of first dose) in which case the death was considered an event.

Time frame: Parts 1 and 2: From start of treatment to end of the study (approximately 3 years 7 months)

Overall Survival (OS): Parts 1 and 2

OS was defined as the time from the date of first dose until death due to any cause. If a participant was not known to have died, survival was censored at the date of last contact. Analysis was performed using Kaplan-Meier method.

Time frame: Parts 1 and 2: From start of treatment to end of the study (approximately 3 years 7 months)

Minimal Residual Disease (MRD) Negativity Rate Per IMWG Sequencing Criteria: Parts 1 and 2

MRD negativity rate was defined as the percentage of participants with negative MRD (assessed by central laboratory) per IMWG sequencing criteria at any time from the date of first dose until the first documentation of confirmed PD, death or start of new anticancer therapy, whichever occurred first. Sequencing MRD negative included: 1) CR: negative immunofixation on serum and urine, disappearance of any soft tissue plasmacytomas and \<5% plasma cells in BMA. If the only measurable disease is by serum FLC levels, CR was defined as normal serum FLC ratio of 0.26 to 1.65; 2) Absence of clonal plasma cells by next generation sequencing (NGS) on BMA in which presence of a clone was defined as \<2 identical sequencing reads obtained after DNA sequencing of BMA using the LymphoSIGHT platform (or validated equivalent method) with a minimum sensitivity of 1 in 10\^5 nucleated cells.

Time frame: Parts 1 and 2: From start of treatment to end of the study (approximately 3 years 7 months)

Pre- and Post-dose Concentrations of Elranatamab: Parts 1 and 2

Time frame: Parts 1 and 2: Till study completion approximately 3 years 7 months

Number of Participants With Anti-Drug Antibody (ADA) and Neutralizing Antibody (Nab) Against Elranatamab: Parts 1 and 2

Time frame: Parts 1 and 2: From start of treatment to end of the study (approximately 3 years 7 months)