Morphological and molecular risk markers for coexistent adenocarcinoma in low-grade dysplastic areas of high-grade adenomatous polyps

Background: Safe and effective endoscopic resection (ER) relies on the endoscopic diagnosis of large lesions to predict the risk of invasive cancer. However, a detailed evaluation of histopathological features and the molecular profile of the polypoid dysplastic mucosa to predict coexistent invasive neoplasm is not available. Design: Data from endoscopic resection of colorectal superficial neoplastic lesions performed at a UK tertiary referral center (2011-2016) were analyzed. A subset of these lesions containing high-grade dysplasia (HGAP), intramucosal or invasive cancer was identified and subjected to a detailed analysis: endoscopic type, ulceration, distribution of high-grade dysplasia, dysplastic nuclear grade, presence and distribution of necrosis, and distribution of tumor-infiltrating lymphocytes (TIL). The two highest morphological grade were microdissected from each lesion and used for DNA extraction and next-generation sequencing using a 24-gene panel (Qiagen, Hiden, Germany). Genetic abnormalities for each locus were categorized by genetic impact according to its severity (low/moderate/high/modifier) and allele frequency. Results: ER was performed for 418 large (≥20mm) colorectal superficial neoplastic lesions (mean size 55.2mm, range 20mm-160mm), 81% being laterally spreading tumors (LST). The proportions harboring an area of invasive cancer by morphological subtype were as follows: LST (non-granular 30.8%, granular mixed 12.3%, granular homogeneous 0.9%) and Is/Isp 11.4%. There was no locoregional/distant recurrence in any patient deemed to have undergone curative ER. The histopathological genetic evaluation was available in 70 cases; a coexistent adenocarcinoma significantly correlated with dysplastic adenomatous mucosa featuring ulceration, mixed interface/interstitial TIL, multifocal high nuclear grade, infiltrative edges, and multifocal intraluminal necrosis. Multifocal intraluminal necrosis and high nuclear grade in the low-grade dysplastic mucosa were driven by cooperative genetic abnormalities of high-impact (FLT4), moderate impact (KRAS/NRAS for infiltrative edges, FLT4, TP53, ERBB2), and low impact (FGFR3, PDGFA). Conclusions: Low-grade areas of HGAP are characterized by cooperative genetic mutations. A subset of markers identifies a risk of coexistent adenocarcinoma, closely correlating with angiogenesis (FLT4), receptor activation (RAS/ERBB2), genome maintenance (TP53), stromal reaction (FGFR3, PDGFRA), and morphology (nuclear grade, necrosis, and inflammation).