To verify the correlation between SSP and BTZ sensitivity, PHGDH expression was examined in CD138+ plasma cells from a small set (n = 6) of multiple myeloma patients isolated either at diagnosis, during therapy or after relapse from various therapeutic interventions (Fig. 5f, Additional file 1: Figure S3e, f and Table S1). The gene discussed is PHGDH; the disease is plasma cell myeloma.