A Study of LY4175408 in Participants With Advanced Cancer

Inclusion Criteria

• Have one of the following advanced or metastatic solid tumor cancers:
• Non-small cell lung cancer (NSCLC)
• Small cell lung cancer (SCLC)
• Endometrial cancer
• Triple negative breast cancer (TNBC) (characterized by HR-negative disease and HER2-negative expression according to American Society of Clinical Oncology (ASCO) - College of American Pathologists guidelines).
• Received all standard therapies for which the individual was deemed to be an appropriate candidate by the treating investigator; OR the individual is refusing the remaining most appropriate standard of care treatment; OR there is no standard therapy available for the disease.
• Eastern Cooperative Oncology Group (ECOG) performance status of ≤1.
• For dose optimization/dose and expansion cohorts (Cohort A2, Cohort B): Measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1.

Exclusion Criteria

• Prior treatment with a protein tyrosine kinase 7 (PTK7) antibody-drug conjugate (ADC) with a topoisomerase I inhibitor as payload (prior therapy with a PTK7 ADC with a non-topoisomerase I inhibitor payload OR non-PTK7 ADC with any payload is permitted).
• Any serious unresolved toxicities from prior therapy.
• Individual with known or suspected history of uncontrolled central nervous system (CNS) metastases.
• Individual with active uncontrolled systemic bacterial, viral, fungal, or parasitic infection.
• Significant cardiovascular disease.
• Prolongation of QT interval corrected for heart rate using Fridericia's formula (QTcF) > 470 milliseconds (ms)
• History of pneumonitis/interstitial lung disease.
• Individuals who are pregnant, breastfeeding, or plan to breastfeed during the trial or within 30 days of the last dose of trial intervention.