⁃ Participant must be able to understand the study procedures

• Patient is, in the investigator's opinion, willing and able to comply with the protocol requirements.

• Patient has given voluntary written informed consent before performance of any study-related procedure nor part of normal medical care, with the understanding that consent may be withdrawn by the patient at any time without prejudice to their future medical care.

• Relapse multiple myeloma patients that have received at least 1 and no more than 3 prior lines of therapy. Induction, intensification with high-dose melphalan and stem cell transplant and maintenance is considered one line of treatment.

• Patients must be refractory to lenalidomide. Refractoriness is defined as progression while receiving lenalidomide or in the first 60 days after the last dose of lenalidomide.

• Refractoriness would be defined regardless of the dose of lenalidomide received, and the schedule or whether it was given alone or in combination.

• Patients can have received prior treatment with proteasome inhibitors. Patients with prior bortezomib treatment are eligible regardless of refractory status. Prior carfilzomib treatment is allowed, provided that the patients achieve at least a partial response to prior carfilzomib, and that there is a treatment free interval of at least 6 months.

• Participant must have a measurable secretory disease defined as either serum monoclonal protein of ≥ 0,5 g/dl or urine monoclonal (light chain) protein ≥ 200 mg/24 h. For patients whose disease is only measurable by serum FLC, the involved FLC should be ≥ 10mg/L (100 mg/dl), with an abnormal serum FLC ratio.

• Participant must have an Eastern Cooperative Oncology Group (ECOG) performance status of ≤ 2

• Participant must be ≥ 18 years of age

• Participant must have adequate organ function. Laboratory values that define adequate organ function for inclusion in study are as follow:

• HEMATOLOGIC Absolute neutrophil count (ANC) ≥1.5 X 109/L Hemoglobin ≥8.0 g/dL (prior red blood cell (RBC) transfusion or recombinant human erythropoietin use is permitted) Platelets ≥75 x 109/L for subjects in whom \<50% of bone marrow nucleated cells are plasma cells; otherwise platelet count \>50 × 10\*9/L (prior platelet transfusion is permitted up to 7 days before the screening phase) Calcium corrected serum calcium \<14 mg/dL (\<3.5 mmol/L); or free ionized calcium \<6.5 mg/dL (\<1.6 mmol/L); HEPATIC Total bilirubin ≤1.5X ULN (Isolated bilirubin ≥1.5xULN is acceptable if bilirubin is fractionated and direct bilirubin \<35%) ALT ≤2.5 X ULN AST ≤2.5 X ULN

• RENAL eGFRa ≥40 mL/min/ 1.73 m2 Spot urine (albumin/creatinine ratios) \<500 mg/g (56 mg/mmol) OR Negative/trace (if ≥1+ only eligible if confirmed ≥ 500 mg/g (56 mg/mmol) by albumin/creatinine ratio (spot urine from first void) Urine Dipstick

• CARDIAC LVEF (echo) ≥ 40%

⁃ Female participants: contraceptive use should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies. A female participant is eligible to participate if she is not pregnant or breastfeeding, and at least one of the following conditions applies:

∙ Is not a woman of childbearing potential (WOCBP) OR

‣ Is a WOCBP and using a contraceptive method that is highly effective (with a failure rate of \<1% per year), preferably with low user dependency, during the intervention period and for at least 4 months after the last dose of study intervention and agrees not to donate eggs (ova, oocytes) for the purpose of reproduction during this period. The investigator should evaluate the effectiveness of the contraceptive method in relationship to the first dose of study intervention.

⁃ A WOCBP must have a negative highly sensitive serum pregnancy test (as required by local regulations) within 72 hours before the first dose of study intervention.

⁃ The investigator is responsible for review of medical history, menstrual history, and recent sexual activity to decrease the risk for inclusion of a woman with a nearly undetected pregnancy.

⁃ Nonchildbearing potential is defined as follows (by other than medical reasons):

‣ ≥45 years of age and has not had menses for \>1 year

‣ Patients who have been amenorrhoeic for \>2 years without history of a hysterectomy and oophorectomy must have a follicle stimulating hormone value in the postmenopausal range upon screening evaluation

‣ Post-hysterectomy, post-bilateral oophorectomy, or post-tubal ligation.Documented hysterectomy or oophorectomy must be confirmed with medical records of the actual procedure or confirmed by an ultrasound. Tubal ligation must be confirmed with medical records of the actual procedure.

⁃ Male participants: contraceptive use should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.

⁃ Male participants are eligible to participate if they agree to the following from the time of first dose of study until 6 months after the last dose of belantamab mafodotin to allow for clearance of any altered sperm:

⁃ \- Refrain from donating sperm

⁃ PLUS either:

‣ Be abstinent from heterosexual intercourse as their preferred and usual lifestyle (abstinent on a long term and persistent basis) and agree to remain abstinent OR

‣ Must agree to use contraception/barrier as detailed below:

• Agree to use a male condom, even if they have undergone a successful vasectomy and female partner to use an additional highly effective contraceptive method with a failure rate of \<1% per year when having sexual intercourse with a WOCBP (including pregnant females).

⁃ All prior treatment-related toxicities (defined by National Cancer Institute- Common Toxicity Criteria for Adverse Events (NCI-CTCAE), version 4.0 must be ≤ Grade 1 at the time of enrolment except for alopecia

⁃ Participant must be able to understand the study procedures and agree to participate in the study by providing written informed consent