The main purpose of this study is to find out whether the study drug, LY4050784, is safe, tolerable and effective in participants alone or in combination with other anticancer agents. In addition, with locally advanced or metastatic solid tumors with a BRG1 (Brahma-related gene 1, also known as SMARCA4) alteration who have previously received, do not qualify for, or are refusing standard of care treatments, or there is no standard therapy available for the disease. The study is conducted in two parts - phase Ia (dose-escalation) and phase Ib (dose-optimization, dose-expansion). The study will last up to approximately 4 years.

This study is researching an investigational drug called marlotamig (REGN7075) by itself and in combination with cemiplimab with or without chemotherapy. The study is focused on patients with certain solid tumors that are in an advanced stage.

The aim of the study is to see how safe and tolerable marlotamig is by itself and in combination with cemiplimab (with or without chemotherapy), and to find out what is the best dose of marlotamig to be given to patients with advanced solid tumors when combined with cemiplimab (with or without chemotherapy). Another aim of the study is to see how effective marlotamig by itself, or in combination with cemiplimab (with or without chemotherapy), is at treating cancer patients.

The study is also looking at:

* Side effects that may be experienced by people taking marlotamig by itself and in combination with cemiplimab with or without chemotherapy
* How marlotamig works in the body by itself and in combination with cemiplimab with or without chemotherapy
* How much marlotamig is present in the blood when given by itself and in combination with cemiplimab with or without chemotherapy
* To see if marlotamig by itself and in combination with cemiplimab with or without chemotherapy works to treat cancer by controlling the proliferation of tumor cells to shrink the tumor
* Whether the body makes antibodies against the study drugs (marlotamig and cemiplimab) (which could make the drug less effective or could lead to side effects)

This is an international phase III trial, with a Bayesian design, incorporating two sequential randomisations. It efficiently examines a series of questions that routinely arise in the sequencing of treatment. The study design has evolved from lengthy international consultation that has enabled us to build consensus over which questions arise from current knowledge and practice. It will enable potential randomisation for the majority of patients with inguinal lymph node metastases and will provide data to inform future clinical decisions.

InPACT-neoadjuvant patients are stratified by disease burden as assessed by radiological criteria. Treatment options are then defined according to the disease burden strata. Treatment is allocated by randomisation. Patients may be allocated to one of three initial treatments:

A. standard surgery (ILND); B. neoadjuvant chemotherapy followed by standard surgery (ILND); or C. neoadjuvant chemoradiotherapy followed by standard surgery (ILND).

After ILND, patients are defined as being at low or high risk of recurrence based on histological interpretation of the ILND specimen. Patients at high risk of relapse are eligible for InPACT-pelvis, where they are randomised to either:

P. prophylactic PLND Q. no prophylactic PLND