Full or intensity‐reduced high‐dose melphalan and single or double autologous stem cell transplant with or without bortezomib consolidation in patients with newly diagnosed multiple myeloma

Objective A post hoc subgroup analysis of two phase III trials (NCT00416273, NCT00416208) was carried out to investigate the influence of 100/140 and 200 mg/m² melphalan as well as single/double autologous stem cell transplantation (ASCT) on progression‐free survival (PFS). Additionally, the effect of bortezomib consolidation on PFS was analyzed. Methods Following induction therapy and high‐dose melphalan with subsequent ASCT, patients with newly diagnosed multiple myeloma (NDMM) were randomized 1:1 to either four 35‐day cycles of bortezomib consolidation (1.6 mg/m² IV on days 1, 8, 15, 22) or observation. Results Of the 340 patients included in this analysis, 13.5% received 1 × MEL100/140, 22.9% 2 × MEL100/140, 31.2% 1 × MEL200, and 32.4% 2 × MEL200. With higher cumulative melphalan dose, PFS improved (P = .0085). PFS curves of patients treated with 2 × MEL100/140 and 1 × MEL200 were very similar. The superior dose effect of MEL200 over MEL100/140 was non‐existent in the bortezomib consolidation arm but pronounced in the observation arm (P = .0015). Similarly, double ASCT was only beneficial in patients without bortezomib consolidation (P = .0569). Conclusions Full dose melphalan and double transplantation seem advantageous only as long as patients are not receiving bortezomib consolidation afterwards.