Mutational heterogeneity in large B-cell lymphoma: insights from paired biopsies

Introduction: Large B-cell lymphoma (LBCL) exhibits striking clinical and molecular heterogeneity. New approaches have emerged to explore tumor heterogeneity and classify LBCL into biological categories. Consequently, the informational requirements from diagnostic samples to provide the necessary information have increased, but the adequacy of single-site biopsies to provide such information is largely unknown. Here we describe spatial and temporal intra-patient variations in the mutational landscape of paired biopsies. Methods: Paired biopsies from 30 patients with LBCL were obtained from spatially distinct sites at the time of primary diagnosis before treatment and/or at a subsequent relapse. The samples were sequenced using a custom designed 59-gene next generation sequencing (NGS) lymphoma panel. Results: Differences in detected mutations of pathogenic or likely pathogenic significance were frequent both when comparing paired diagnostic biopsies, 2/6 (33%), and when comparing paired biopsies at primary diagnosis and relapse, 8/16 (50%). Mutational heterogeneity tended to increase with longer time interval between biopsies. Analysis of paired diagnostic and relapse biopsies revealed that certain clones present at diagnosis disappeared, while new clones emerged at relapse. Notably, TP53 mutations were detected in six out of seven patients in an extranodal location. In two cases, TP53 mutation was only detected in the relapse biopsy. Several of the mutations identified in this study are used or under investigation as targets for cancer treatments. Conclusion: Multi-site biopsies revealed spatial and temporal mutational heterogeneity in patients with LBCL. Our findings indicate that mutational differences between biopsy pairs can occur at all timepoints examined. This underscores the necessity of performing repeat biopsies with each relapse to capture the full spectrum of genetic aberrations.