Cellular Proliferation By Multiplex Immunohistochemistry Identifies Aggressive Disease Behavior in Relapsed Multiple Myeloma

Background: As treatment options in relapsed and refractory multiple myeloma (MM) increase, prognostic biomarkers are needed to aid clinical decision making. The plasma cell labeling index (PCLI) has been a validated prognostic tool in MM but utilization remains limited due to technical burden. A novel multiplex immunohistochemical (mIHC) co-staining technique for CD138 and Ki67 expression was developed to quantify plasma cells in active cycling: the Plasma Cell Proliferation Index (PCPI). Previously presented results from newly diagnosed patients (pts) demonstrated an elevated PCPI is associated with shorter progression-free (PFS) and overall survival (OS) in pts undergoing first line MM treatment. Here we assess MM pts with PCPI both at diagnosis and relapse to assess the impact of cell cycling ratio at relapse on outcomes with subsequent therapy and overall clinical course.