Does Response to Bortezomib-Based Therapies Correlate to Beta-2 Microglobulin in Multiple Myeloma?

Introduction. Multiple Myeloma (MM) is a heterogeneous, incurable disease. Several prognostic scores have been developed to estimate response to treatment, progression free survival (PFS) and overall survival (OS). The International Staging System defines 3 stages with distinct prognostic significance, using serum beta 2 microglobulin (b2M) and serum albumin. However, due to a higher power of risk discrimination, current guidelines recommend to stratify patients according to cytogenetics (CG) and treat high-risk patients with Bortezomib (BZ)-based therapies.

In Uruguay, BZ is financed and regulated by a National Funding Board and is approved for high-risk MM or renal impairment at diagnosis or at relapse. As a consequence, the patients included in this study are a selected high risk MM subgroup.

Even though proteasome inhibitors have improved outcomes for many high-risk MM patients, some still present short response duration and poor survival. Identifying simple factors that can predict response to BZ would be useful in order to better select the most appropriate therapeutic choice.

Patients and Methods. We conducted a retrospective study to evaluate MM response to BZ-based therapy according to b2M, serum creatinin (Cr) and CG. Forty-seven MM patients [median age 59 years (38-77), females 25 (53%)] from two public centers treated with BZ-based combinations were included. According to local regulatory policies, only patients with renal failure and/or high risk CG features received BZ as first line therapy (n=31). Other 16 individuals received BZ combinations for relapsed/refractory disease. Patients received a median of 5 cycles of BZ (3-6). Nineteen individuals (40%) received high dose melphalan and autologous stem cell transplantation after BZ-based induction. At diagnosis, 28 (59%) had an ISS 3, 24 (51%) patients had serum Cr higher than 2 mg/dL and 14 (30%) exhibited high risk CG. Responses to BZ therapy were evaluated according with International Myeloma Working Group criteria as complete response (CR), very good partial response (VGPR), partial response (PR), stable disease (SD) and progressive disease (PD). Responses were analyzed depending on b2M level, serum Cr and CG. Comparison between groups was made by chi-square test. PFS and OS were calculated by the Kaplan-Meier method. Survival was compared between groups by log-rank test.

Results. No differences in responses to BZ-based therapies were found when comparing patients with low (lower than 5,5 mg/L) versus high b2M levels (CR/VGPR 44,4 vs 44% respectively, p=0.97), low versus high serum Cr (CR/VGPR 34 vs 55% respectively, p=0.18) and standard versus high risk CG (CR/VGPR 46,7 vs 38,5% respectively, p=0.62). Patients with renal failure (serum Cr 2 mg/dL or higher at diagnosis, n=23) had a median of 53% (0 - 88%) reduction in Cr levels after receiving at least three cycles of BZ therapy. Eleven of them (47,8%) had normal renal function after completing BZ treatment. From 9 patients requiring dyalisis at diagnosis, 4 were out of dyalisis after BZ treatment. No significant differences in PFS and OS were observed when patients with low versus high b2M levels and standard versus high risk CG were compared. Patients with low Cr levels at diagnosis show a significantly better OS compared with those with Cr higher than 2 mg/dL (median OS not reached versus 42 months respectively, p=0.004), with no differences in PFS.

Conclusion. In a selected high risk MM patients group treated with BZ-based therapies, similar response rates were obtained in individuals with high or low b2M levels, Cr levels, and standard or high risk CG. Although individuals with renal failure at diagnosis exhibit similar quality of responses than standard patients, long term OS of this group is still impaired and further improvements in therapy are needed.

Note: GB and ER have contributed in equal parts to this work.