Spatial Heterogeneity in Large Resected Diffuse Large B-Cell Lymphoma Bulks Analysed by Massively Parallel Sequencing of Multiple Synchronous Biopsies

SIMPLE SUMMARY: Substantial genetic heterogeneity was described within large tumour masses of several cancer entities. However, this topic has not been addressed in patients with diffuse large B-cell lymphoma (DLBCL). Therefore, we collected multiple biopsies of twelve patients who had diagnostic or therapeutic resections of large lymphoma bulks and analysed 213 genes known to be important for lymphoma biology. The biopsies of each patient were compared to investigate the spatial heterogeneity in DLBCL. Ten out of twelve patients had discordant mutations which were not present in all of their biopsies and similar results were seen by the analysis of copy number variants. Some of the involved genes have a known prognostic and therapeutic relevance in DLBCL. This shows that single biopsies underestimate the complexity of the disease and might overlook possible mechanisms of resistance and therapeutic targets. ABSTRACT: Diffuse large B-cell lymphoma (DLBCL) usually needs to be treated immediately after diagnosis from a single lymph node biopsy. However, several reports in other malignancies have shown substantial spatial heterogeneity within large tumours. Therefore, we collected multiple synchronous biopsies of twelve patients that had diagnostic or therapeutic resections of large lymphoma masses and performed next-generation sequencing of 213 genes known to be important for lymphoma biology. Due to the high tumour cell content in the biopsies, we were able to detect several mutations which were present with a stable allelic frequency across all the biopsies of each patient. However, ten out of twelve patients had spatially discordant mutations and similar results were found by the analysis of copy number variants. The median Jaccard similarity coefficient, a measure of the similarity of a sample set was 0.77 (range 0.47–1), and some of the involved genes such as CARD11, CD79B, TP53, and PTEN have a known prognostic or therapeutic relevance in DLBCL. This shows that single biopsies underestimate the complexity of the disease and might overlook possible mechanisms of resistance and therapeutic targets. In the future, the broader application of liquid biopsies will have to overcome these obstacles.