To evaluate the clinical application value in bone marrow protection of Trilaciclib in the neoadjuvant treatment of stage II/III classic osteosarcoma in combination with pirarubicin and lobaplatin.

Classic osteosarcoma is the most common primary bone malignancy. At present, osteosarcoma is usually treated with preoperative chemotherapy, surgical operation and postoperative chemotherapy. Treatment with preoperative chemotherapy is also known as neoadjuvant chemotherapy. Neoadjuvant chemotherapy has brought benefits to patients, but safety concerns are inevitable. Myelosuppression is a major factor affecting the compliance of patients treated by chemotherapy. Patients with chemotherapy-induced myelosuppression(CIM) have higher rates of infection, sepsis, bleeding, and fatigue, resulting in hospitalization, hematopoietic growth factor support, blood transfusions (red blood cells and/or platelets) and even death. In addition, CIM often leads to dose reduction and delayed administration, which limits the therapeutic dose intensity and therefore affects the anti-tumor efficacy of chemotherapy.

Currently, there are no approved treatments in osteosarcoma to prevent chemotherapy-induced cell damage. Although some treatments may help to address CIM when it occurs such as blood transfusions and growth factors, these treatments are pedigree specific, being used after hematopoietic stem progenitor cells damage and could bring additional toxicity.

Trilaciclib is a highly effective, selective and temporarily reversible inhibitor of CDK4/6. The proliferation of bone marrow hematopoietic stem cells depends on CDK4/6 activity. Bone marrow hematopoietic stem cells are blocked in the G1 phase of the cell cycle after exposure to Trilaciclib before chemotherapy is given.

Therefore, this study is conducted to evaluate the clinical application value in bone marrow protection of Trilaciclib in the neoadjuvant treatment of stage II/III classic osteosarcoma in combination with pirarubicin and lobaplatin.

Inclusion Criteria:

1. Written informed consent signed;
2. Classic osteosarcoma confirmed by histopathology (high grade);
3. Newly diagnosed stage Ⅱ-Ⅲ based on Enneking staging criteria;
4. Planned to receive neoadjuvant chemotherapy;
5. Measurable disease on CT by RECIST 1.1.
6. No antitumor system therapy received;
7. ECOG 0-1
8. Adequate organ function.
9. Females of childbearing potential as well as males and their partners must agree to use an effective form of contraception during the study and for 6 months following the last dose of study medication.

Exclusion Criteria:

1. History of malignancies of other type;
2. Allergic to study agent;
3. History of psychotropic substance abuse, alcohol or drug use;
4. The researchers considered inappropriate to join the study of any cause.