A Phase 3 Randomized, Open Label, Multicenter Study to Evaluate the Safety and Efficacy of ABBV-706 versus Standard of Care in Subjects with Relapsed/Refractory Small Cell Lung Cancer (SCLC)

Small cell lung cancer (SCLC) is characterized by aggressive and rapid growth and a
tendency to develop early spread to distant sites including mediastinal lymph nodes,
liver, bones, adrenal glands, and brain. The purpose of this study is to assess safety,
tolerability, and change in disease activity of ABBV-706 compared to standard of care
(SOC) treatment (topotecan, lurbinectedin, or amrubicin).

ABBV-706 is an investigational drug being developed for the treatment of SCLC. There are
two treatment arms in this study. Participants will either receive ABBV-706 or SOC.
Approximately 531 adult participants will be enrolled in the study across 175 sites
worldwide.

Participants with SCLC will receive intravenous (IV) ABBV-706 or SOC [topotecan (IV or
orally), or lubinectedin (IV), or amrubicin (IV)]. The estimated duration of the study is
approximately 53 months.

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 and may require frequent medical assessments, blood tests, questionnaires, and
scans.

Inclusion Criteria:

- Diagnosis of histologically or cytologically confirmed Relapsed/Refractory (R/R)
Small Cell Lung Cancer (SCLC).

- Participants must have progressed on prior systemic therapy, with CPI (if eligible)
and prior tarlatamab, defined as:

- In the 1L and 2L setting respectively, platinum-based chemotherapy (i.e.,
carboplatin or cisplatin and etoposide with CPI, if eligible for CPI) and 2L
tarlatamab; or

- In the 1L and 2L setting, platinum-based chemotherapy (i.e., carboplatin and
etoposide with atezolizumab and lurbinectedin in combination with atezolizumab
maintenance and 2L tarlatamab; or

- In the 1L setting, platinum-based chemotherapy (i.e., carboplatin or cisplatin
and etoposide with CPI if eligible) in combination with tarlatamab in frontline
induction and/or maintenance

- Participants must be considered suitable to receive SOC comparator (topotecan,
lurbinectedin, or amrubicin).

- Participants must have an Eastern Cooperative Oncology Group (ECOG) Performance
Status of 0 to 1 during the screening period prior to the first dose of study
treatment.

- Participants must have measurable disease per Response Evaluation Criteria in Solid
Tumors (RECIST) v1.1. Target lesions situated in a previously irradiated area are
considered measurable if progression has been demonstrated in such lesions.

- Participants with brain metastasis from an extracranial solid tumor are eligible if
the brain metastases are:

- Previously treated and not requiring anticonvulsants and steroids for at least
7 days prior to first dose of study treatment. If required for management,
subjects on a steroid equivalent of prednisone dose of ≤ 10 mg/day are eligible
or;

- Untreated and asymptomatic not requiring anticonvulsants and steroids for at
least 7 days prior to the first dose of study treatment. If required for
management, subjects on a steroid equivalent of prednisone of ≤ 10 mg/day are
eligible.

Exclusion Criteria:

- Participants with known active/symptomatic central nervous system metastases.

- Participants with a history of interstitial lung disease (ILD) or pneumonitis that
previously required treatment with systemic steroids, or any evidence of active
ILD/pneumonitis on screening chest computed tomography (CT) scan.

- Participants with any clinically significant conditions that would adversely affect
the participation in the study, and the subject should have a life expectancy of at
least 3 months.

- Participants who have received prior treatment with a seizure-related 6 homolog
(SEZ6) targeted Antibody drug conjugate (ADC), other targeted ADCs, or any other
investigational agent not including tarlatamab in 1L.

- Participants who have received prior treatment with any Top1i such as topotecan,
irinotecan, belotecan, camptothecin, rubitecan, exatecan or locally approved
topoisomerase I inhibitor (Top1i) payload.