This study aims to realize an economic evaluation of the introduction of Plerixafor in addition to G-CSF and alternative options, in patients with multiple myeloma (MM) who failed or insufficiently mobilize peripheral blood stem and progenitor cells in response to G-CSF alone.

Inclusion Criteria:

• Adult patients diagnosed with Multiple Myeloma who were eligible for high-dose melphalan supported with autologous hematopoietic stem cell transplantation (HSCT) as part of their treatment plan
• First mobilization attempt
• "rhG-CSF alone" mobilization regimen
• Failed mobilization as documented by an increase in CD34+ cell mobilization deemed insufficient to initiate apheresis (below 15/µL), after the 4 first injections of rhG-CSF that are administered in the evening

Exclusion Criteria:

• Age < 18 years;
• Primary diagnosis other than MM
• 2nd or subsequent mobilization attempt
• Patients who previously received HDCT + autologous HSCT
• Chemotherapy-based mobilization regimen
• Efficient mobilization, allowing for apheresis and collection of the target cell number (5x106 CD34+ cells/kg for every planned autologous transplantation as per institutional SOPs).

The study will retrospectively review 60 electronic health records of patients who underwent peripheral blood stem cell mobilization for Multiple Myeloma, and who failed to achieve efficient and clinically meaningful mobilization in response to a well-conducted "G-CSF alone" regimen.