Efficiency of Automated and Manual Plasma Cell Immunoselection for FISH Analysis in Multiple Myeloma

Multiple myeloma (MM) is a heterogeneous plasma cell (PC) malignancy in both clinical presentation and genetic profile. Cytogenetic characterization, particularly by interphase fluorescence in situ hybridization (FISH), is critical for risk stratification and treatment decisions. FISH results depend on the PC infiltration rate in bone marrow (BM); therefore, CD138-positive immunoselection is required to overcome reduced FISH sensitivity due to low infiltration. We evaluated the performance of automated PC immunoselection compared to the manual method.

We retrospectively analyzed data from 715 BM samples sent for routine FISH testing between 2019 and 2024. PCs were isolated manually (n = 351) or automatically (n = 364). BM infiltration was assessed by flow cytometry (FC) and/or cytomorphology. FISH analysis was performed using a primary panel with three DNA probes or an expanded panel with additional probes. Confirmed diagnoses were obtained from clinical records.

FISH was successfully performed in 81% of samples, with automated processing achieving a higher success rate (86% vs. 75%, p < 0.001). Automated processing provided higher PC yields, enabling testing with expanded probe sets. Chromosomal abnormalities were detected in more than 90% of confirmed MM cases, regardless of isolation method. PC infiltration strongly predicted FISH success, with infiltration of ≥ 3% corresponding to an 80% probability of successful FISH.

Automated immunoselection improves PC yield, enabling broader FISH testing compared to manual processing. Information on PC infiltration obtained by cytomorphology or FC, which indicates sample quality, can support quality assessment in the cytogenetics laboratory.