Abstract
Post-pubertal testicular germ-cell tumours (TGCTs) can present with a variety of distinct histologies which are nevertheless lineage related and often co-occurring. The exact lineage relationships and developmental pathways leading to the different histologies is debated. In order to investigate the relationship of histologic populations, mate-pair sequencing (MPseq) and exome sequencing (ExomeSeq) were conducted on different histological populations within the same tumour. Ten TGCTs with 1-3 histologic types/tumour were sequenced. Junctions of somatic chromosomal rearrangements were identified on a per genome basis, with germ cell neoplasia in situ possessing the least (median 1, range 0-4) and embryonal carcinoma the most (median 8.5, range 6-12). Copy number variation revealed gains and losses, including isoform 12p (i12p) (10/10 samples), and chromosomes 7, 8, and 21 gains (7/10 samples). Mapping of shared junctions within a tumour revealed lineage relationships, but only i12p was shared between patients. ExomeSeq from two cases demonstrated a high level of copy-neutral loss of heterozygosity. Parallel assessment of separate histologies within a single TGCT demonstrated cumulative and divergent changes, suggesting the importance of parallel sequencing for detection of relevant biomarkers.