Comparing Toxicities and Survival Outcomes with Total Therapy 4 (TT4) for 70-Gene (R70)-Defined Low-Risk Multiple Myeloma (MM) to Results Obtained with Total Therapy 3 Protocols TT3A and TT3B

TT3, incorporating bortezomib and thalidomide with induction prior to and consolidation after melphalan 200mg/m2-based transplants and 3 year maintenance with VTD (year 1) and TD (years 2+3) in TT3A and with VRD for 3 years in TT3B resulted in a high CR rate of ∼60% and, in the 85% of patients with GEP-defined low-risk MM, 5-yr OS/EFS of 80%/78%; 5-year CR duration estimate was 88%.

Phase III trial TT4 for low-risk MM randomized patients between standard (S) and light (L) arms. TT4-L applied 1 instead of 2 cycles of induction therapy with M-VTD-PACE prior to and 1 instead of 2 cycles of consolidation with dose-reduced VTD-PACE after tandem transplantation. M-VTD-PACE comprised melphalan, bortezomib, thalidomide, dexamethasone and 4-day continuous infusions of cisplatin, doxorubicin, cyclophosphamide, etoposide. TT4-S applied standard single dose melphalan 200mg/m2, while TT4-L used a 4-day fractionated schedule of melphalan 50mg/2 on days 1–4. VRD maintenance for 3 years was identical in both arms. Here we report, for both TT4 arms combined, on grade >2 mucosal toxicities, applying CTCAE version 3.0, and on efficacy (CR, EFS, OS) in relationship to TT3 in low-risk MM. At the time of analysis, median follow-up on TT4 is 10.7 months and on TT3A/B 62.3/33.4 months. To facilitate comparisons between trials with different follow-up times, TT3 data were backdated to follow-up time comparable to TT4 as of this reporting time.

Baseline characteristics were similar in TT3 (n=364) and TT4 (n=165) in terms of B2M both >=3.5mg/L and >5.5mg/L, and elevated levels of CRP, creatinine, and LDH. Presence of cytogenetic abnormalities (CA) overall and in terms of CA13/hypodiploidy was similar in both. Fewer TT4 patients had ISS-1 (31% v 43%, P=0.010) and more had hemoglobin <10g/dL (35% v 26%, P=0.029). While neither trial had GEP-defined high-risk in the 70-gene model (R70), the more recently validated R80 distribution showed 7% high-risk in TT4 v 3% in TT3 (P=0.031). DelTP53 was more prevalent in TT4 than TT3 (39% v 10%, P<0.001), and MY favorable subgroup designation pertained to 3% in TT4 v 12% in TT3 (P=0.002). Toxicities are reported per protocol phase. During induction (TT4, n=160; TT3, n=364), grade >2 mucosal toxicities included colitis in 0%/1% (P=0.32), esophagitis/dysphagia in 0%/1% (P=0.33), GI mucositis, NOS in 1%/1% (P=0.99) and stomatitis/pharyngitis in 0%/1% (P=0.99). With transplant-1, (TT4, n=139; TT3, n=344), grade >2 mucosal toxicities included colitis in 3%/1% (P=0.24), esophagitis/dysphagia in 1%/5% (P=0.03), gastritis in 1%/0% (P=0.29), GI mucositis, NOS in 1%/2% (P=0.73) and stomatitis/pharyngitis in 0%/5% (P=0.008); with transplant-2 (TT4, n=105; TT3, n=294), grade >2 mucosal toxicities included colitis in 4%/3% (P=0.77), esophagitis/dysphagia in 0%/2% (P=0.20), GI mucositis, NOS in 2%/3% (P=0.99) and stomatitis/pharyngitis in 0%/1% (P=0.58). With consolidation (TT4, n=85; TT3, n=280), grade >2 mucosal toxicities included colitis in 0%/3% (P=0.36) and GI mucositis, NOS in 0%/1% (P=0.99). Timing of onset and final levels of CR differed substantially between TT4 and TT3 in favor of TT4 (P=0.006); no differences were observed in OS (P=0.36), EFS (P=0.66), and CR duration (P=0.12).

TT4 (both arms combined) provided, despite higher proportions of patients with unfavorable characteristics than in TT3, superior CR rate and comparable survival outcomes to TT3's low-risk population. GI toxicities were reduced in TT4 v TT3. Results of TT4 arms will be presented.

No relevant conflicts of interest to declare.