With the existing recombinant human granulocyte colony-stimulating factors (G-CSFs) patents expiring and the FDA approval of new biosimilar and innovator biologics, patients being treated with Grade III and IV myelosuppressive chemotherapy regimens will have additional therapeutic options. This observational study will describe the patient characteristics of new users of G-CSFs. It will describe in the treatment cohorts a primary outcome of hospitalizations for febrile neutropenia. The BBCIC will use the findings from this descriptive analysis to design a comparative study evaluating the real-world effectiveness and safety of biosimilar and innovator G-CSFs.