Trilaciclib, an innovative first-in-class therapy that protects bone marrow at the source, has been approved for use in CDK4/6-independent small-cell lung cancer. However, clinical practice shows that patients with solid tumors frequently experience treatment-related pancytopenia involving neutrophils, erythroid lineage, and platelets after antineoplastic therapy, with a particularly high incidence of grade 3-4 myelosuppression. This poses serious threats to patient safety and delays the timely, standard administration of anticancer treatments. Therefore, it is imperative to investigate the expansion of trilaciclib's indications to solid tumors and its underlying mechanisms, and to establish a primary prophylaxis prediction model for solid tumor patients receiving chemotherapy.

This study is designed in three parts:

1. Retrospective study: Collect real-world clinical data from patients with solid tumors who received trilaciclib for bone marrow protection during antineoplastic therapy, identify relevant multifactorial determinants, and use statistical methods to develop Primary Prophylaxis Prediction Model A.
2. Prospective study: Based on Model A, patients will be allocated into two experimental cohorts. Experimental Cohort 1: patients for whom primary prophylaxis with trilaciclib is indicated per Model A will receive primary prophylactic treatment. Experimental Cohort 2: patients for whom primary prophylaxis with trilaciclib is not indicated per Model A will receive secondary prophylaxis according to protocol. Outcomes will include the incidence of grade 3-4 myelosuppression, factors potentially influencing trilaciclib's marrow-protective effect, objective response rate (ORR) and progression-free survival (PFS) over 4-6 cycles, and changes in immunologic parameters.
3. Mechanistic exploration: Factors identified by the prediction model as influencing the need for trilaciclib primary prophylaxis will serve as mechanistic targets. Through in vivo and in vitro experiments using flow cytometry and single-cell sequencing, we will validate trilaciclib's bone marrow-protective effects across animal models of solid tumors with varying CDK4/6 dependence, and assess changes in tumor efficacy endpoints, T-lymphocyte subsets, and tumor immune microenvironment markers following trilaciclib monotherapy or combination with standard anticancer regimens.

Inclusion Criteria:

• patients for whom primary prophylaxis with trilaciclib is indicated per Model A will receive primary prophylactic treatment.

Exclusion Criteria:

• patients for whom primary prophylaxis with trilaciclib is not indicated per Model A will receive secondary prophylaxis according to protocol.