Multiple myeloma (MM) is a malignant disease of plasma cells characterized by the uncontrolled proliferation of myeloma cells in the bone marrow (BM), which disrupts normal hematopoiesis and can lead to severe complications. The disease most commonly develops from monoclonal gammopathy of undetermined significance (MGUS), which is usually asymptomatic. The diagnosis of MM relies on the collection of BM samples via aspiration or biopsy, followed by cytomorphological examination, immunophenotyping by flow cytometry, and chromosomal abnormality analysis using fluorescence in situ hybridization (FISH). FISH enables the detection of clinically significant chromosomal abnormalities that influence prognosis and therapeutic decision-making. However, its application often faces challenges, such as the uneven distribution of plasma cells in BM, dilution of the sample with peripheral blood (hemodilution), and certain disease subtypes that do not infiltrate the BM. We analyzed the success of FISH testing in patients with suspected MM and examined the correlation between the results of cytomorphological examination, flow cytometry, and FISH. Additionally, we compared the efficiency of manual and automated plasma cell immunoselection. The study included 811 patients treated at the Specialized Hematology Laboratory (SHL) between 2019 and 2023. The results showed that immunoselection was successful in 83% of patients, while in the remaining 17%, FISH testing could not be performed due to an insufficient number of plasma cells in the BM sample. Among patients with confirmed MM, the success rate of immunoselection was 98%, indicating that FISH testing was not feasible in only 2% of cases with confirmed MM. In 15% of samples analyzed with the DNA probe panel, no chromosomal rearrangements were detected. However, among patients with confirmed MM, the proportion of negative FISH results was significantly lower (2%). The comparison of manual and automated plasma cell immunoselection revealed no statistically significant differences in the success rate of FISH testing or the number of DNA probes used. We also confirmed that both flow cytometry and cytomorphological assessment are significant predictors of FISH test outcomes. The results of cytomorphological BM examination were identified as a critical predictor of immunoselection success, as patients with more than 10% plasma cell infiltration in the BM had a significantly higher likelihood of successful FISH testing and positive results. Furthermore, the proportion of plasma cells obtained through cytomorphological analysis was significantly correlated with the number of DNA probes used. In conclusion, FISH testing is essential for the diagnosis and management of patients with MM, as it enables the precise detection of chromosomal abnormalities. Although the overall success of this method is high, its application in certain patients is hindered by the low plasma cell concentration in BM samples.
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