Cancer is a condition where cells in a specific part of body grow and reproduce uncontrollably. Non-Small Cell Lung Cancer (NSCLC) is a solid tumor, a disease in which cancer cells form in the tissues of the lung. The purpose of this study is to evaluate the safety and efficacy (how well the study drug works against the disease) of ABBV-637 alone or in combination with docetaxel/osimertinib in participants with solid tumors (NSCLC). Adverse events and change in disease activity will be assessed.

ABBV-637 is an investigational drug being developed for the treatment of solid tumors. Study consists of 3 parts - monotherapy dose escalation (Part 1), combination dose escalation and expansion (Parts 2a and 2b) with docetaxel and combination dose escalation and expansion (Parts 3a and 3b) with osimertinib. Approximately 109 adult participants with relapsed/refractory (R/R) solid tumors will be enrolled in approximately 30 sites across the world.

In Part 1, participants with solid tumors will receive intravenous (IV) ABBV-637 in 28-day cycles. In Part 2a and 2b, participants will receive IV ABBV-637 in combination with IV docetaxel in 28-day cycles. In Part 3a and 3b, participants will receive intravenous (IV) ABBV-637 in combination with daily oral tablets of osimertinib in 28-day cycle.

There may be higher treatment burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the study at a hospital or clinic. Treatment effects will be monitored by medical assessments, blood tests, side effect reporting, and questionnaires.

Inclusion Criteria:

• Histologic solid tumor diagnosis (Part 1).
• For Part 2 docetaxel combination therapy: EGFR WT expressing relapsed/refractory (R/R) non-small cell lung cancer (NSCLC) participants.
• For Part 3 osimertinib combination therapy: mutEGFR-expressing RR NSCLC participants.
• Measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1.
• Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1.
• For Part 1 only - history of R/R disease that has progressed on all standard of care therapy.
• For Part 2 only - history of RR NSCLC that has progressed after treatment with platinum-based chemotherapy regimen and either immune checkpoint inhibitor or targeted therapy and may not have been treated with prior single agent chemotherapy.
• For Part 3 only - history of RR NSCLC that has progressed on osimertinib
• Meet the laboratory values as described in the protocol.

Exclusion Criteria:

• History (within 6 months) of congestive heart failure (defined as New York Heart Association, Class 2 or higher), ischemic cardiovascular event, cardiac arrhythmia requiring pharmacological or surgical intervention, pericardial effusion, or pericarditis.
• Unresolved Grade 2 or higher toxicities related to previous anticancer therapy except alopecia.
• For Part 3 only: History of interstitial lung disease (ILD) or pneumonitis that required treatment with systemic steroids, nor any evidence of active ILD or pneumonitis.