This clinical trial is focused on studying a type of lung cancer known as Extensive Stage Small Cell Lung Cancer (ES-SCLC). The study is evaluating a treatment called Trilaciclib, which is given to patients before they receive a chemotherapy drug named Topotecan. The purpose of the study is to see if Trilaciclib can help patients live longer compared to those who receive a placebo before Topotecan. A placebo is a substance with no active medication, used for comparison in clinical trials.

Participants in the study will receive either Trilaciclib or a placebo before their Topotecan chemotherapy sessions. The study will monitor the overall survival of patients, which means the length of time patients live after starting the treatment. The trial will also look at other factors, such as how the cancer responds to the treatment and any side effects that may occur. The study is designed to last for a period of up to 120 days, during which patients will receive regular intravenous infusions of the study medications.

In addition to Trilaciclib and Topotecan, the study involves the use of other substances like Sodium Chloride and Glucose Monohydrate, which are commonly used in medical settings to support the administration of intravenous treatments. The trial aims to provide valuable information on the effectiveness and safety of using Trilaciclib in combination with Topotecan for treating patients with ES-SCLC.