Molecular monitoring of residual myeloma cells after allogeneic stem cell transplantation. (A) Cumulative relapse risk according to molecular status. ○ represents PCR-negative patients; ×, PCR-mixed patients; and •, PCR-positive patients. (B) Molecular follow-up. Unique patient numbers are on the left. • indicates PCR-positive; ○, PCR-negative; R, relapse; and ✠, death.