Multiple myeloma (MM) is the second most commonly diagnosed hematological malignancy, characterized by the proliferation of malignant plasma cells in the bone marrow and excessive production of immunoglobulins (1, 2). In recent years, as new therapies including immunomodulators (IMiDs), proteasome inhibitors (PIs) and monoclonal antibodies (mAbs) have been incorporated into standard treatments, the overall survival (OS) and progression-free survival (PFS) of MM have been significantly improved. However, most cases still remain a chronic and incurable disease due to its typical pattern of remission and relapse (3–6). Heterogeneous cytogenetic abnormalities are the most important characteristics of MM and cytogenetic analysis is essential for prognostic evaluation at diagnosis (7). Many studies had identified that some cytogenetic abnormalities including del(17p)(p53), t(4;14)(p16;q32), t(14;16)(q32;q23), and t(14;20)(q32;q12) were high-risk abnormalities (HRA) in MM patients, and others such as del(13q) and t(11;14)(q13;q32) were considered as standard-risk factors, whereas the prognostic value of 1q21 gain/amplication (gain/amp 1q21) had been controversial (8–13). Of note, most of the previous studies mainly focused on the prognostic impact of the abnormalities identified at diagnosis, only few studies had considered the significance of the new acquired cytogenetic aberrations throughout the course of the disease (14–16). A longitudinal cytogenetic study focusing on cytogenetic evolution of 128 patients from the time of primary diagnosis and at relapse from Merz et al. (17) revealed that the presence of a new acquired HRA during follow-up conferred to poor prognosis as well. The study from Binder et al. (7) showed that the development of additional abnormalities during the 3 years following diagnosis was associated with increased subsequent mortality. While these previous studies had highlighted the importance of ongoing monitoring of MM cytogenetic signatures, they were not sufficient to adequately assess all potentially HRA that occur during the disease process in the case of modern therapies. For example, it is unclear whether HRA emerged at diagnosis or during follow-up has different effects on the outcome of MM patients. In addition, longitudinal studies on cytogenetic evolution in Chinese MM patients are still lacking. Therefore, in the present study, we summarized the clinical data of 230 newly-diagnosed MM (NDMM) patients admitted to our hospital, focusing on the analysis of 100 cases with sequential FISH data, with the aim to emphasize the importance of continuous monitoring of the cytogenetic characteristics and shed light on the implications of cytogenetic clonal evolution in Chinese MM patients.

The prognostic significance of baseline cytogenetic aberrations in NDMM is well-documented, which have been shown to have a significantly greater prognostic impact in MM than mutations in specific genes (19) and there is increasing evidence that the evolution of cytogenetic aberrations over time has an adverse effect on the prognosis of MM patients (20–22). The study from Aleksander et al. (23) showed that presence of clonal evolution, particularly the acquisition of new del(17p) at relapse negatively affect the outcome of MM, and similar results were observed in the Lakshman et al. (24) study. The study from Binder et al. (7) enrolled 989 MM patients including 304 with at least twice cytogenetic evaluations showed that the presence of t(11;14) at the time of diagnosis was associated with decreased odds of cytogenetic evolution during follow-up, while the presence of at least one trisomy or tetrasomy was associated with increased odds, and the development of additional abnormalities during the 3 years following diagnosis was associated with increased subsequent mortality. In addition, they also found that the prognostic significance of baseline cytogenetic abnormalities was most pronounced at the time of diagnosis and attenuated over time, the presence of cytogenetic high-risk features at diagnosis were associated with shorter OS but the presence of high-risk features were no longer associated with OS in those who survived 3 years after diagnosis, which highlighted the importance of continuous monitoring of cytogenetic characteristics and suggested that risk factors emerged at different times in the disease process may have different prognostic implications for MM patients. As more and more data suggest that disease progression, dissemination, and relapse in MM is driven by clonal evolution (25–28), an evolving consensus to reevaluate for cytogenetic high-risk features during follow-up has been reached, but the clinical implication of cytogenetic clonal evolution especially the prognostic significance of de novo HRA remains to be further clarified.

Our study revealed that 49% of Chinese MM patients acquired de novo FISH abnormalities during follow-up, and de novo FISH aberrations were associated with disease progression regardless of HRA or non-HRA (83.7% vs. 56.9%, X² = 0.003) and they were also conferred to an inferior median PFS (31 vs. 51 months, p = 0.032). In addition, the patients with 2 or more de novo FISH abnormalities had shorter median PFS (median 24 vs. 45 months, p = 0.003) when compared to those with one or no de novo FISH abnormality, and patients who acquired new abnormalities within 31 months since diagnosis had significantly worse PFS (median: 20 vs. 41 months, p < 0.001) and OS (median: 61 vs. 100 months, p = 0.008) compared to those who acquired new abnormalities after 31 months. Since clonal evolution may reflect the genomic instability, which is the hallmark of all neoplastic diseases and is the source of genetic heterogeneity of MM, it is reasonable to speculate that the more new emerging cytogenetic anomalies and the earlier new FISH abnormalities acquired, the greater the tumor instability and the worse the prognosis of MM. Consistent with this conjecture, our study showed that the higher number of de novo FISH abnormalities, the worse the survival, suggesting a cumulative adverse effect of the number of de novo FISH aberrations.

Although cytogenetic risk stratification of MM patients is widely used in clinical practice, there are some controversies about the prognostic impact of HRA in MM patients as new treatment strategies are constantly updated. Related study reported that with appropriately treatments, the survival of patients with certain high risk categories can approach that of patients with standard risk disease. In a large trial using bortezomib-based induction, early ASCT, and bortezomib maintenance, the median OS of patients with del(17p) was approximately 8 years (8-year survival rate of 52%), which was identical to patients with standard risk MM. In contrast, survival was lower for patients with t(4;14) (8-year survival rate, 33%) and for patients with gain(1q21) (8-year survival rate, 36%). These findings underscore the limitations of current risk stratification models in the context of modern therapy and highlight the need to stratify MM based on individual cytogenetic groups rather than arbitrary heterogeneous risk categories (29, 30). Considering the impact of the number of cytogenetic abnormalities on prognosis, Binder et al. (31) found that the greater the number of HRA at the time of diagnosis, the worse the prognosis of MM patients. In our study, almost all patients received modern therapies such as bortezomib, immunomodulator or ASCT as induction or maintenance, and no significant difference in PFS (median 37 vs. 49 months, p = 0.187) and OS (median 91 vs. 107 months, p = 0.381) were observed between the patients with 1 HRA and those without HRA, but the patients with ≥2 HRA had shorter median PFS (28 vs. 49 months, p = 0.038) and OS (75 vs. 107 months, p = 0.040) than the patients without HRA, suggesting by modern strategies of therapy, only two or more HRA were definitely adverse prognostic factor in Chinese MM patients, which highlighted the potential for risk stratification to change as treatments were updated.

In the era of new drugs, the role of ASCT has been questioned. However, ASCT remains the standard treatment recommended by international guidelines, including those of the American Society of Clinical Oncology and the European Society for Medical Oncology (32). Our study did not demonstrate that ASCT could improve the prognosis of high-risk patients (those who acquired new cytogenetic abnormalities during follow-up). We speculate that the limited number of patients undergoing ASCT in our cohort may have introduced statistical bias. In future studies, we plan to collect more cases to further explore this issue.

The ability to draw firm conclusions from our data is limited by the retrospective nature and a relatively small number of enrolled patients, but our results reaffirm the importance of continuous monitoring of the cytogenetic characteristics of MM during follow-up. De novo FISH abnormalities during follow-up are adverse prognostic factors in MM patients, especially when ≥2 new FISH anomalies are presented, and the presence of ≥2 HRA during the disease process are associated with poor survival in Chinese MM patients, which remains to be further confirmed in larger scale of studies.

Re-evaluation of cytogenetic characteristics by serial FISH tests is important in MM patients. De novo FISH abnormalities during follow-up are adverse prognostic factors, especially when ≥2 new FISH anomalies and acquired new abnormalities within 31 months since diagnosis are presented, and the presence of ≥2 HRA during the disease process are associated with poor survival in Chinese MM patients.