Abstract

Background: Childhood cancer survivors treated with radiation therapy (RT) are at an increased risk of subsequent precancerous and cancerous lesions, including the risk of early invasive colorectal carcinoma (CRC). It is well-established that radiation-associated CRC undergo a preinvasive dysplastic stage where they can be detected and managed by early colonoscopy. Molecular profiling of radiation-associated polyps using targeted Next Generation Sequencing (NGS) is highly sensitive and specific and may aid in unraveling their molecular composition. In this study, we aim to analyze and molecularly characterize colorectal adenomatous polyps in young cancer survivors treated with RT using a targeted NGS panel, as well as correlate the genetic findings with their histomorphology.

Design: We extracted DNA scrolls from 18 polyps of different histomorphologies which we acquired from 17 patients who received RT for childhood cancers. The median age is 35 at the time of colonoscopy. The NGS panel comprises more than 146 hotspots in more than 30 genes including: BRAF, KRAS, TP53, PIK3CA, PTEN and CTNNB1 etc. Four of the polyps had histopathologic diagnoses of sessile serrated lesion (SSL) (22.2%), while the remaining 14 polyps were either tubular adenomas (TA), tubulovillous adenomas (TVA) or TA with submucosal invasion (77.7%). High-risk features were defined as size of 10 mm or greater, three or more adenomas, tubulovillous or villous histology or adenomas with high-grade dysplasia.

Results: Five polyps elucidated hotspot mutations at cancer-associated genes (27.7%), while the remaining 13 polyps were negative for the mutations tested (72.3%). Of the 5 mutated polyps, 2 polyps harbored substitution mutations in the KRAS gene at exon 2. The two polyps were non-serrated and showed high-risk histological features. Additionally, two other polyps showed substitution mutations in the BRAF gene at codon V600E, with both polyps showing histological features of SSL. The last mutated polyp had a histological diagnosis of TA with submucosal invasion and elucidated a substitution mutation at the TP53 gene.

Conclusion: This retrospective study is one of the first to molecularly characterize colorectal adenomatous polyps in childhood cancer survivors treated with radiation therapy using Next Generation Sequencing. Our molecular analysis demonstrate that radiation-induced polyps harbor similar genetic changes to dysplastic adenomatous polyps in the average-risk population. We postulate that radiation-associated polyps follow the conventional 'adenoma-carcinoma’ pathway or the alternative ‘serrated’ sequence, making them amenable to detection and management by early colonoscopy. Furthermore, our NGS panel failed to detect novel driving mutations in cancer-associated genes. More comprehensive molecular analysis of these polyps is required to understand their molecular composition and to aid in identifying actionable genetic alterations.

Keywords: Colorectal Polyp; Cancer Survivor; Radiation Therapy; Mutation Analysis; Next-Generation Sequencing; Molecular Pathology

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