Dose-Escalation Study of ABBV-838, an Antibody Drug Conjugate, in Subjects With Relapsed and Refractory Multiple Myeloma

Inclusion Criteria:

- Eastern Cooperative Oncology Group Performance Status of 0 to 2

- Not eligible for stem cell/bone marrow transplant or have refused stem cell/bone
marrow transplant or have relapsed after autologous or allogeneic stem cell/bone
marrow transplant

- Eligible for and agree to BM aspirate prior to treatment start

- Measurable disease M component in serum (≥ 0.5 g/dL) and/or urine (≥ 0.2 g excreted in
a 24 hour collection sample)

- Must have received at least 3 prior lines of therapy including a proteasome inhibitor
and an immunomodulatory agent or those who are double refractory to a PI and an
immunomodulatory agent and have demonstrated disease progression (DP) on or within 60
days of completion of the last therapy; participants previously treated with an
alkylating agent, in addition to an IMiD or proteasome inhibitor, are allowed to
enroll in the trial

- Participants must have adequate liver, kidney, and bone morrow function

- Participants with a history of chronic heart failure must have cardiac ECHO indicating
left ventricular ejection fraction (LVEF) ≥ 45% within 21 days prior to first dose of
study drug

- Participants in the combination therapy arms must be eligible to receive
pomalidomide/dexamethasone, bortezomib/dexamethasone or lenalidomide/dexamethasone or
other approved agents per current prescribing information for MM.

- Participants who will receive combination therapy with Pomalidomide/Dexamethasone must
have received at least two prior therapies including lenalidomide and a proteasome
inhibitor and have demonstrated disease progression on or within 60 days of completion
of the last therapy

Exclusion Criteria:

- Received anti-cancer therapy including chemotherapy, immunotherapy, radiation,
biologic, any investigational therapy or herbal therapy within a period of 21 days
prior to the first dose of ABBV-838, and have unresolved toxicities ≥ grade 2

- Concurrent metastatic solid tumors

- Non-Measurable M Protein (serum or urine) and measurable sFLC (< 100 mg/mL)

- Major surgery within 21 days prior to the first dose of ABBV-838

- Clinically significant uncontrolled condition(s) including but not limited to the
following:

Grade ≥ 3 peripheral neuropathy or grade 2 peripheral neuropathy with pain Uncontrolled
hypercalcemia Active uncontrolled infection Symptomatic congestive heart failure Unstable
angina pectoris or cardiac arrhythmia Psychiatric illness/social situation that would limit
compliance with the study

- Major immunologic reaction to any IgG containing agent or auristatin based agent

- Participants who are taking strong CYP3A4 inhibitors

- Positive for HIV (Human Immunodeficiency Virus) or with active hepatitis B and/or C

- Corneal pathology that would limit evaluation of loss in visual acuity associated with
corneal deposits.

- Prior exposure to pomalidomide for subjects enrolling in the
pomalidomide/dexamethasone combination arm.