Use of molecular diagnostic methods for lymphoma staging in bilateral bone marrow biopsies*

Background: Testing for immunoglobulin and T-cell-receptor gene rearrangement is a useful adjunct to morphologic evaluation of bone marrow involvement by non-Hodgkin's lymphoma. At this institution, each sample from a patient undergoing bilateral bone marrow sampling for lymphoma staging is assayed separately to avoid possible false negatives from dilution, if, for example, only one sample is positive. Methods and Results: Gene rearrangement results were reviewed for 140 patients, to assess if pooling the two aspirate samples from bilateral biopsies could be implemented. Discordant results between right and left iliac crest samples were found in 4 of 140 (2.9%) patients. Morphologic assessment was performed for 138 of the 140 patients. In 64 cases there were no abnormal findings. Four of these 64 (6.3%) had monoclonality demonstrated by genotyping or immunophenotyping. Of 134 patients for which both tests were performed, 17 (12.7%) showed discordance: 6 were negative by immunophenotyping, positive by genotyping (3 cases with malignant morphology, 1 with suspicious morphology, and 2 without evidence of malignancy); 11 positive by phenotyping but not genotyping (6 cases with malignant morphology, 3 with suspicious morphology, and 2 without evidence of malignancy). Conclusions: These findings support the role for these ancillary studies; in some cases both may be needed to demonstrate monoclonality. Based on this low occurrence of discordant findings between right and left samples, we feel that bilateral specimens can be pooled without unacceptable risk of false negatives due to possible dilution.