Inclusion Criteria:

          1. Written informed consent signed in accordance with federal, local, and institutional
             guidelines.

          2. Age greater than or equal to (≥) 18 years at the time of informed consent.

          3. Histologically confirmed diagnosis with measurable disease for relapsed/refractory
             myeloma.

          4. Symptomatic MM, based on IMWG guidelines.

          5. Patients must have measurable disease as defined by at least one of the following:

               1. Serum M-protein ≥ 0.5 gram per deciliter (g/dL) by serum protein electrophoresis
                  (SPEP) or, for immunoglobulin A (IgA) myeloma, by quantitative IgA

               2. Urinary M-protein excretion at least 200 mg/24 hours

               3. Serum free light chain (FLC) ≥ 100 milligram per liter (mg/L), provided that FLC
                  ratio is abnormal

               4. If SPEP is felt to be unreliable for routine M-protein measurement (example, for
                  IgA MM), then quantitative immunoglobulin (Ig) levels by nephelometry or
                  turbidometry are acceptable

          6. Any non-hematological toxicities (except for peripheral neuropathy as described in
             exclusion criterion #22) that patients had from treatments in previous clinical
             studies must have resolved to less than or equal (≤) Grade 2 by C1D1.

          7. Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤ 2.

          8. Adequate hepatic function within 28 days prior to C1D1:

               -  For SPd, SRd, and SPEd: Total bilirubin < 2* upper limit of normal (ULN) (except
                  patients with Gilbert's syndrome [hereditary indirect hyperbilirubinemia] who
                  must have a total bilirubin of ≤ 3* ULN) and both aspartate aminotransferase
                  (AST) and alanine aminotransferase (ALT) < 2.5* ULN

               -  For SVd, SPVd, SDd, SNd, SBd and SDPd: Total bilirubin of < 1.5* ULN (except
                  patients with Gilbert's syndrome [hereditary indirect hyperbilirubinemia] who
                  must have a total bilirubin of ≤ 3* ULN) and both AST and ALT < 2.0* ULN

               -  For SKd: Total bilirubin < 2* ULN (except patients with Gilbert's syndrome
                  [hereditary indirect hyperbilirubinemia] who must have a total bilirubin of ≤ 3*
                  ULN) and both AST and ALT < 3.0* ULN

          9. Adequate renal function within 28 days prior to C1D1. Estimated creatinine clearance
             (CrCl) calculated using the formula of Cockroft and Gault (1976):

               -  ≥ 20 milliliter per minute (mL/min) for SVd, SDd, and SKd arms

               -  ≥ 30 mL/min for SNd and SBd arms

               -  ≥ 45 mL/min for SPd, SPVd, SPEd and SDPd arms

               -  > 60 mL/min for SRd arm

         10. Adequate hematopoietic function within 28 days prior to C1D1: total white blood cell
             (WBC) count ≥ 1,500/millimeter cube (mm^3), absolute neutrophil count (ANC) ≥
             1,000/mm^3, hemoglobin (Hb) ≥ 8.0 g/dL, and platelet count ≥ 100,000/mm^3.

               -  SPVd (Arm 4) and SKd (Arm 6) only: platelet count ≥150,000.

         11. Female patients of childbearing potential must have a negative serum pregnancy test at
             Screening. Female patients of childbearing potential and fertile male patients must
             use highly effective methods of contraception throughout the study and for 1 week
             following the last dose of study treatment.

             SPd (Arm 1) Only:

         12. Relapsed or refractory MM with:

               1. Documented evidence of progressive disease (PD) after achieving at least stable
                  disease (SD) for ≥ 1 cycle during a previous MM regimen (i.e., relapsed MM)

               2. ≤ 25 percent (%) response (i.e., patients never achieved ≥ MR) or PD during or
                  within 60 days from the end of the most recent MM regimen (i.e., refractory MM)

               3. Previously undergone ≥ 2 cycles of lenalidomide and a PI (in separate therapeutic
                  regimens [not for maintenance] or in combination)

               4. In the expansion arm at RP2D, patients must not be pomalidomide refractory

             SVd (Arm 2) Only:

         13. Relapsed or refractory MM with:

               1. Documented evidence of relapse after ≥ 1 previous line of therapy

               2. Not refractory to bortezomib in their most recent line of therapy

             SRd in RRMM (Arm 3) Only:

         14. Patients who received ≥ 1 prior therapeutic regimen (prior lenalidomide is allowed as
             long as patient's MM was not refractory to prior lenalidomide; patients whose MM was
             refractory to lenalidomide maintenance regimens will be allowed in this cohort).

             SPVd (Arm 4) Only:

         15. Patients who received 1- 3 prior lines of therapy, including ≥ 2 cycles of
             lenalidomide and have demonstrated disease progression on their last therapy (may
             include prior bortezomib, as long as the patient's MM was not refractory to bortezomib
             therapy), but patients must be pomalidomide-naïve in the Dose Expansion at RP2D
             (Cohort 4.3 ONLY).

             SDd (Arm 5) Only:

         16. Patients who received ≥ 3 prior lines of therapy, including a PI and an
             immunomodulatory agent (IMiD), or patients with MM refractory to both a PI and an
             IMiD.

         17. Patients must not have received prior anti-cluster of differentiation 38 (anti-CD38)
             monoclonal antibodies (Cohort 5.3 ONLY - Dose Expansion at RP2D).

             SKd (Arm 6) Only:

         18. Patients may have received prior PIs; however, their MM must NOT be refractory to
             carfilzomib.

             SRd in NDMM (Arm 7) Only:

         19. Patients must have symptomatic myeloma per IMWG guidelines with either CRAB criteria
             (calcium elevation, renal failure, anemia, lytic bone lesions) or myeloma-defining
             events and need systemic therapy. No prior systemic therapy for NDMM is permitted
             other than pulse dose dexamethasone (maximum dose of 160 mg) or corticosteroid
             equivalent.

             SNd (Arm 8) Only:

         20. Patients must have MM that relapsed after 1 - 3 prior lines of therapy (may not
             include those with MM refractory to bortezomib or carfilzomib but patients must be
             ixazomib-naïve).

             SPEd (Arm 9) Only:

         21. Patients who received ≥ 2 prior therapies, including lenalidomide and a proteasome
             inhibitor (in separate or the same regimens), but patients must be pomalidomide-naive
             and elotuzumab-naive in the Dose Expansion at RP2D (Cohort 9.3 ONLY).

             SBd (Arm 10) Only:

         22. Patients who have MM that was refractory to an IMiD, a proteasome inhibitor, and
             refractory or intolerant (or both) to an anti-CD38 monoclonal antibody. Patients must
             be belantamab mafodotin-naive in the Dose Expansion cohort at RP2D (Cohort 10.3 ONLY).

        SDPd (Arm 11) Only:

        Patients who received 1-3 prior therapies, including lenalidomide and a proteasome
        inhibitor (in separate or the same regimen), but patients must be pomalidomide-naive and
        daratumumab-naive in the Dose Expansion cohort at RP2D (Cohort 11.3 ONLY).

        Exclusion Criteria:

        Patients meeting any of the following exclusion criteria are not eligible to enroll in this
        study:

          1. Smoldering MM.

          2. MM that does not express M-protein or FLC (i.e., non-secretory MM is excluded), and
             quantitative immunoglobulin levels cannot be used instead.

          3. Documented active systemic amyloid light chain amyloidosis.

          4. Active plasma cell leukemia.

          5. Red Blood Cell (RBC) and platelet transfusions and blood growth factors within 14 days
             of C1D1.

          6. Radiation, chemotherapy, or immunotherapy or any other anticancer therapy ≤ 2 weeks
             prior to C1D1, and radio-immunotherapy within 6 weeks prior to C1D1. Patients on
             long-term glucocorticoids during Screening do not require a washout period. Prior
             radiation is permitted for treatment of fractures or to prevent fractures as well as
             for pain management.

          7. Patients with history of spinal cord compression with residual paraplegia (Dose
             Escalation Phase only).

          8. Treatment with an investigational anti-cancer therapy within 3 weeks prior to C1D1.

          9. Prior autologous stem cell transplantation < 1 month, or allogeneic stem cell
             transplantation < 3 months prior to C1D1.

         10. Active graft versus host disease after allogeneic stem cell transplantation.

         11. Life expectancy < 3 months.

         12. Major surgery within 4 weeks prior to C1D1.

         13. Active, unstable cardiovascular function:

               1. Symptomatic ischemia, or

               2. Uncontrolled clinically-significant conduction abnormalities (e.g., patients with
                  ventricular tachycardia on antiarrhythmics are excluded; patients with 1st degree
                  atrioventricular (AV) block or asymptomatic left anterior fascicular block/right
                  bundle branch block (LAFB/RBBB) will not be excluded), or

               3. Congestive heart failure (CHF) of New York Heart Association (NYHA) Class ≥ 3, or

               4. Myocardial infarction (MI) within 3 months prior to C1D1

               5. Ejection fraction (EF) < 50% at Screening

         14. Uncontrolled active hypertension.

         15. Uncontrolled active infection requiring parenteral antibiotics, antivirals, or
             antifungals within one week prior to first dose.

         16. Known active hepatitis A, B or C.

         17. Known human immunodeficiency virus (HIV) infection or HIV seropositivity.

         18. Any active gastrointestinal dysfunction that prevents the patient from swallowing
             tablets or interferes with absorption of study treatment.

         19. Currently pregnant or breastfeeding.

         20. A serious active psychiatric or active medical condition which, in the opinion of the
             Investigator, could interfere with treatment.

         21. Hypersensitivity to any of the treatments for the arm in which the patient is
             enrolled.

         22. SVd Arm (Arm 2), SPVd (Arm 4), and SNd Arm (Arm 8) only: Prior history of neuropathy
             Grade > 2, or Grade ≥ 2 neuropathy with pain at Screening (within 28 days prior to
             C1D1).

         23. Patients who are eligible for the selinexor PK Run-in only: Treatment with moderate or
             strong inhibitors/inducers of CYP3A within 7 days prior to Day 1 of the PK Run-in
             period.

         24. Patients who are eligible for the selinexor PK Run-in only: Not able to receive a
             strong CYP3A4 inhibitor due to concomitant medications.

         25. SKd arm only: HBs Ag + plus HBc Ab + even though no active hepatitis B virus (HBV)
             hepatitis. If HBs Ag - plus HBc Ab +, treating physician needs to contact the medical
             monitor.

         26. Prior exposure to a selective inhibitor of nuclear export (SINE) compound, including
             selinexor.

             SBd (Arm 10): Only:

         27. Current corneal epithelial disease except mild punctate keratopathy.