Cases presenting onset of identical lymphoid malignancy in both donor and recipient after allogeneic hematopoietic stem cell transplantation. Seven cases of apparent transmission of a premalignant clone after transplantation of stem cell material (hematopoietic stem cell transplantation) or DLI. A red arrow from donor to recipient indicates the malignant clone was identified in stored material before onset of disease. Red bars specify transplant from related donor; blue bars specify transplant from unrelated donor. The text on the right indicates the molecular evidence of related clonal disease between the 2 patients in each case. DLI, donor leukocyte infusion; MZL, marginal zone lymphoma; TCR, T-cell receptor; rear., rearrangement; VNTR, variable number tandem repeats.