The Prognostic Impact of Plasma Cell Chromosome 17 Abnormality Percentage Cut-offs on Patient Outcomes in Multiple Myeloma

Abstract Abnormalities in chromosome 17 encompassing the TP53 locus [deletion of the small arm {del (17p)} and monosomy 17] as identified by fluorescent in-situ hybridization (FISH), are a well-established adverse prognostic factor in multiple myeloma (MM). Previous research suggested that higher percentages of these chromosome 17 abnormalities correlate with worse prognoses, proposing various cutoff points to assess this relationship, ranging between 50-60%. Of note, these studies employed extensive plasma cell enrichment protocols and often included only cases with high plasma cell percentages (70-90%). Our study aims to investigate the relationship between the percentage of plasma cells with chromosome 17 abnormalities and patient outcomes at the time of acquisition of the abnormality, scrutinizing various cut-off points for prognostic significance. We retrospectively reviewed 339 MM patients at our institution, including newly diagnosed and relapsed cases, examining chromosome 17 abnormality levels identified by FISH on bone marrow specimens. After CD138 magnetic bead enrichment, 50 nuclei were scored for these abnormalities and the percentage calculated. It is important to note that the precise percentage of plasma cells in the sample was not quantified. We analyzed survival outcomes across different percentage cut-off points (20%, 40%, 50%, 55%, 60%, and 80%) using Kaplan Meier analysis and log-rank tests. Significant differences in median survival were noted at the 40% and 50% cut-offs. Patients with >40% chromosome 17 abnormalities showed a median survival of 17.5 months compared to 25.8 months for those with ≤40% (p<0.05), an absolute difference of 8.3 months. Similarly, the >50% group had a median survival of 19.4 months versus 24.3 months in the ≤50% group (p<0.05), with an absolute difference of 4.9 months. However, these differences, while statistically significant, may not be clinically substantial. Furthermore, a 55% cut-off did not yield a significant survival difference (23.5 months vs. 19.8 months for ≤55% and >55% groups, p>0.05) in our cohort. Our findings confirm some prognostic value of chromosome 17 abnormality levels in MM but suggest that the absolute differences in median survival at certain cut-offs, based on the test as performed in our laboratory, might not be clinically impactful. This may be due to differences in the proportion of non-plasma cells within the samples being scored, resulting in ambiguity when interpreting FISH results. Future research should aim to improve the consistency of plasma cell enrichment, develop approaches to score only plasma cells, establish risk-specific cut-offs, and explore the relationship between chromosome 17 abnormality levels, treatment response, and overall significance. The study raises important questions about the necessity of stratifying patients based on chromosome 17 abnormality levels versus simply detecting their presence for prognostic assessment.