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 andHER2-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 anappropriate candidate by the treating investigator; OR the individual is refusingthe remaining most appropriate standard of care treatment; OR there is no standardtherapy available for the disease.

• Eastern Cooperative Oncology Group (ECOG) performance status of ≤1.

• For dose optimization/dose and expansion cohorts (Cohort A2, Cohort B): Measurabledisease 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 ADCwith a non-topoisomerase I inhibitor payload OR non-PTK7 ADC with any payload ispermitted).

• 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 parasiticinfection.

• 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 trialor within 30 days of the last dose of trial intervention.