A Study of FOR46 in Patients With Relapsed or Refractory Multiple Myeloma (RRMM)

Inclusion Criteria: * Male or female ≥ 18 years of age * Measurable MM that is relapsed or refractory to established therapies with known clinical benefit in RRMM or intolerant of those established MM therapies. Prior lines of therapy must include a proteasome inhibitor (PI), an immunomodulatory imide drug (IMiD) and a CD38-directed therapy in any order of combination. * ECOG performance status of 0 or 1 * Adequate hematologic, renal and hepatic function * Females of child-bearing potential must have a negative serum pregnancy test and use a medically acceptable form of contraception * Male patients with with female partners of childbearing potential must agree to use 2 effective methods of contraception * Patients must provide signed informed consent Exclusion Criteria: * Persistent clinically significant toxicities from previous anticancer therapy * NCI CTCAE Grade ≥ 2 peripheral neuropathy from any etiology or has a genetic disorder that is associated with peripheral neuropathy even without current neuropathic manifestations * Has received treatment with a stem cell transplant within 12 weeks before administration of patient's first dose of FOR46 * Has had radiation or systemic anticancer therapy within 14 days before first dose of FOR46 * Has received treatment with an investigational drug within 28 days before first dose of FOR46 * Has had a major surgical procedure within 28 days before administration of the patient's first FOR46 dose * Is breastfeeding * Clinically significant cardiovascular disease * Uncontrolled, clinically significant pulmonary disease * Uncontrolled intercurrent illness * Has known positive status for HIV or either active/chronic hepatitis B/C * Requires anticoagulation with warfarin or direct thrombin inhibitor; a washout of 7 days before the administration of a patient's first FOR46 dose is required for patients removed from these treatments * Requires medications that are strong inhibitors or strong inducers of CYP3A4 * Has a history of episodic atrial fibrillation or flutter; patients with chronic atrial fibrillation are not excluded. * Prior treatment with an ADC containing Monomethyl auristatin E (MMAE) or Monomethyl auristatin F (MMAF).