A Study to Assess Adverse Events, and How Intravenously (IV) Infused ABBV-969 Moves Through the Bodies of Adult Participants With Metastatic Castration-Resistant Prostate Cancer

Inclusion Criteria:

• Histological, pathological, and/or cytological confirmation of adenocarcinoma of theprostate.

• Estimated life expectancy > 6 months.

• Must have progressed on prior novel hormonal agents (NHAs) (e.g., abirateroneacetate and/or enzalutamide) for the treatment of metastatic prostate cancer and/orcastration-resistant prostate cancer (CRPC). Determination of progression is doneper local investigator according to Response Evaluation Criteria in Solid Tumors (RECIST), version 1.1 and/or Prostate Cancer Working Group 3 (PCWG3).

• Serum testosterone levels <= 50 ng/dL (<= 1.73 nmol/L) within the screening periodand prior to the first dose of the study drug.

• Must have received at least one NHA (e.g., enzalutamide and/or abiraterone).Additionally, participants must have received at least one taxane for prostatecancer (or have refused, or are intolerant to, or unable to get access to taxanes).

• Must have >= 1 metastatic lesion that is present on baseline computed tomography (CT), magnetic resonance imaging (MRI), or bone scan imaging obtained <= 28 daysprior to beginning study therapy.

• Serum prostate specific antigen (PSA) level >= 1.0 ng/mL.

• Availability of representative baseline tumor tissue (most recent archived tumortissue after any novel hormonal agent (NHA) and/or any Prostate-Specific MembraneAntigen (PSMA) targeted therapy or fresh biopsy collected during screening phase)suitable for immunohistochemistry (IHC) testing. This requirement may be waived atthe discretion of the AbbVie Medical Monitor if collecting a biopsy at screeningwould place the subject at risk of harm or would require a technically complicatedprocedure based on tumor location as assessed by the investigator.

• Laboratory values meeting the criteria laid out in the protocol.

• QT interval corrected for heart rate (QTc) <= 470 msec (using Fridericia'scorrection), no >= Grade 3 arrythmia, and no other clinically significant cardiacabnormalities.

Exclusion Criteria:

• Unresolved Grade 2 or higher toxicities related to previous anticancer therapyexcept alopecia.

• History of other active malignancy, as laid out in the protocol.

• History of interstitial lung disease (ILD) or pneumonitis that required treatmentwith systemic steroids, nor any evidence of active ILD or pneumonitis on screeningchest CT scan.

• History of or active idiopathic pulmonary fibrosis, organizing pneumonia (e.g.,bronchiolitis obliterans), drug-induced pneumonitis, or idiopathic pneumonitis.

• History of or active clinically significant, intercurrent lung-specific illnessesincluding, but not limited to those listed in the protocol.