Purpose: Ovarian high grade serous carcinoma (HGSC) is usually diagnosed at late stage. We investigated whether late-stage HGSC has unique genomic characteristics consistent with acquisition of volutionary advantage compared to early-stage tumours.
Experimental Design: We performed targeted next generation sequencing and shallow whole genome sequencing (sWGS) on pre-treatment samples from 43 patients with FIGO stage I–IIA HGSC to investigate somatic mutations and copy number alterations (SCNA). We compared
results to pre-treatment samples from 52 stage IIIC/IV HGSC patients from the BriTROC-1 study.
Results: Age of diagnosis did not differ between early-stage and late-stage patients (median 61.3 years vs 62.3 years respectively). TP53 mutations were near-universal in both cohorts (89% early-stage, 100% late-stage) and there were no significant differences in the rates of other somatic mutations, including BRCA1 and BRCA2. We also did not observe cohort-specific focal SCNA that could explain biological behaviour. However, ploidy was higher in late-stage (median 3.0) than early-stage (median 1.9) samples. Copy number (CN) signature exposures were significantly different between cohorts, with greater relative signature 3 exposure in early-stage and greater signature 4 in late-stage. Unsupervised clustering based on CN signatures identified three clusters
that were prognostic.
Conclusions: Early stage and late stage HGSC have highly similar patterns of mutation and focal SCNA. However, copy number signature analysis showed that late-stage disease has distinct signature exposures consistent with whole genome duplication. Further analyses will be required to ascertain whether these differences reflect genuine biological differences between early and late-stage or simply time-related markers of evolutionary fitness.