Cytogenetic Progression in Patients with Multiple Myeloma As Assessed By Serial Bone Marrow Biopsy Is Associated with Worse Outcome

Background:Multiple Myeloma (MM) is a hematologic malignancy characterized by the proliferation of clonal, mutated plasma cells, which ultimately leads to multi-organ damage and in most cases death. Despite improved treatments, clinical heterogeneity remains, with some patients succumbing to disease within 1-2 years. Certain cytogenetic and FISH abnormalities at diagnosis confer a higher likelihood of poor outcomes (Mikhael et al., 2013). Still, the utility of repeated cytogenetic assessment over the course of disease is unknown.

Methods: We performed a retrospective review to identify MM patients with cytogenetics (CG) performed at diagnosis who had two or more bone marrow (BM) examinations performed during follow up over a five year period at UW Carbone Cancer Center. We reviewed the pathology and CG results from each BM sample. CG data was categorized into risk groups using the mSMART stratification criteria: High risk - deletion 17p13, t(14;16), t(14;20); intermediate risk - t(4;14), hypodiploid, deletion 13, gain of 1q21; standard risk - hyperdiploidy and all other abnormalities, and normal CG. CG progression over disease course was categorized based on stability or change in CG risk group. We measured survival from date of diagnosis to death or last follow up.

Results: 130 patients with CG at diagnosis were identified over the five year period of the study. These patients had 365 follow-up bone marrow (BM) aspirates, 341 with repeat CG study. Initial cytogenetics were as follows: 90 (69%) of 130 patients had normal CG at diagnosis, 13 (10%) standard risk CG, 16 (13%) intermediate risk CG, and 11 (8%) high risk CG. Serial CG studies showed both development of new CG abnormalities in patients with previously normal studies, and clonal evolution with CG abnormal patients acquiring additional abnormalities on repeat testing. 24 (27%) of 90 patients with normal CG at diagnosis developed abnormal CG during disease course: 12 had intermediate risk CG and 9 high risk CG, the latter all due to p53 deletion. Clonal evolution and drift among initially CG abnormal patients were also common. Of the 34 patients with abnormal CG results on diagnosis and subsequent bone marrow samples, clonal evolution was identified in 19 patients (56%) and 4 (12%) patients developed new CG abnormalities unrelated to the prior clone, while 11 (32%) showed stable CG. Despite this high rate of change, only two patients with abnormal CG at diagnosis moved from a lower to a higher cytogenetic risk group.

When we correlated CG at diagnosis with survival, we found that patients with high risk CG at diagnosis appeared to have shorter median overall survival at 3.8 yrs (range 1-12 yrs) compared with 7.4 yrs (range 2-12 yrs) for intermediate risk, 8.5 yrs (range 2-9 yrs) for standard risk, and 8.2 yrs (range 1-12 yrs) for normal CG. Comparison among all four groups was not statistically significant however, possibly due to the small proportion of high risk CG patients. When we examined the effect of acquiring CG abnormalities, we found that development of abnormal CG in patients with normal CG at diagnosis was associated with shorter median OS (4.0 yrs) compared to either persistent normal CG (11.3 yrs) or any CG abnormality at diagnosis (7.4 yrs), overall comparison p = 0.0048.

Conclusion: Our longitudinal study of 130 unselected patients with MM revealed a cohort who showed cytogenetic progression. In patients with normal CG at diagnosis, the presence of cytogenetic abnormalities in follow-up BM specimens was associated with inferior overall survival. This finding indicates that serial testing may facilitate the detection of a higher risk patient cohort. Further analysis is underway to identify clinical parameters that underlie a higher risk of clonal evolution or development of new cytogenetic abnormalities. The results of our study will help elucidate the optimal prognostic utility of cytogenetic analysis in patient care.