Ultra-deep sequencing detects ovarian cancer cells in peritoneal fluid and reveals somatic TP53 mutations in noncancerous tissues

Abstract

Current sequencing methods are error-prone, which precludes the identification of low frequency mutations for early cancer detection. Duplex sequencing is a sequencing technology that decreases errors by scoring mutations present only in both strands of DNA. Our aim was to determine whether duplex sequencing could detect extremely rare cancer cells present in peritoneal fluid from women with highgrade serous ovarian carcinomas (HGSOCs). These aggressive cancers are typically diagnosed at a late stage and are characterized by TP53 mutations and peritoneal dissemination. We used duplex sequencing to analyze TP53 mutations in 17 peritoneal fluid samples from women with HGSOC and 20 from women without cancer. The tumor TP53 mutation was detected in 94% (16/17) of peritoneal fluid samples from women with HGSOC (frequency as low as 1 mutant per 24,736 normal genomes). Additionally, we detected extremely low frequency TP53 mutations (median mutant fraction 1/13,139) in peritoneal fluid from nearly all patients with and without cancer (35/37). These mutations were mostly deleterious, clustered in hotspots, increased with age, and were more abundant in women with cancer than in controls. The total burden of TP53 mutations in peritoneal fluid distinguished cancers from controls with 82% sensitivity (14/17) and 90% specificity (18/20). Age-associated, low frequency TP53 mutations were also found in 100% of peripheral blood samples from 15 women with and without ovarian cancer (none with hematologic disorder). Our results demonstrate the ability of duplex sequencing to detect rare cancer cells and provide evidence of widespread, low frequency, age-associated somatic TP53 mutation in noncancerous tissue.TP53 mutations | ultra-deep sequencing | ovarian cancer | clonal hematopoiesis | premalignant mutations T he detection of tumor-specific mutations in clinically accessible samples has enormous potential to transform cancer diagnostics, monitoring, and screening. However, a major limitation is insufficiently accurate sequencing methods. Conventional nextgeneration sequencing (NGS) technologies have a high false positive error rate, which precludes reliable detection of mutations at frequencies <1/100 (1). "Molecular tagging" of single-stranded DNA decreases the rate of false mutations to less than 1 per 10,000 sequenced nucleotides and has been successfully applied to the detection of mutant cancer DNA in a variety of clinical samples (2-6). However, this false positive error rate limits the specificity of this method in challenging situations in which ultra-deep sequencing is needed to detect extremely low frequency mutant molecules (e.g., <1/10,000), as is the case of ovarian cancer DNA in Pap smears (5). Because true mutations are indistinguishable from artifacts, compromised specificity leads to lower sensitivity and overall low diagnostic accuracy. Duplex sequencing is an NGS technology that employs molecular tagging of both strands of DNA independently. True mutations are defined as mutations that are present at the same...

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