P301 Non-familial small bowel carcinomas in Crohn's disease: clinico-pathological, molecular and prognostic features

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Background: An increased risk for small bowel carcinoma (SBC) has been reported in Crohn's disease (CrD). We aimed to explore clinical, histopathologic, molecular and prognostic features of CrD-associated SBC (CrD-SBC) in comparison to both coeliac disease (CD)-associated SBC (CD-SBC) and sporadic SBC (spo-SBC).

Methods: Seventy-six patients, who underwent surgical resection for non-familial SBC (25 CrD-SBC26, CD-SBC and 25 spo-SBC), were retrospectively recorded to investigate survival together with histological and molecular features detected by immunohistochemistry, multiplex PCR and sequencing.

Results: CD-SBC showed a significantly (p=0.004) better sex-, age- and stage-adjusted overall and cancer-specific survival in comparison to CrD-SBC, while no significant difference was found between spo-SBC and either CD-SBC or CrD-SBC. CD-SBC exhibited a significantly (p=0.001) higher rate of microsatellite instability (MSI, 65%) compared to both CrD-SBC (16%) and Spo-SBC (16%). The median number of tumor-infiltrating lymphocytes (TIL) correlated with MSI status and was significantly higher in CD-SBC than in both CrD-SBC (p<0.001) and spo-SBC (p=0.002). Among CD-SBC, MSI allowed to separate two subgroups with different outcome, stage and TP53 mutation rate. MSI was the result of MLH1 methylation in all cases (with the exception of one case of CrD-SBC). No BRAF mutation was observed in any SBC. Mutations in KRAS, NRAS, and PIK3CA were detected in 30%, 4% and 13% of cases, respectively. HER2 gene amplification was identified in two CD-SBC, two CrD-SBC and one spo-SBC.

Conclusions: In comparison to CrD-SBC, CD-SBC harbor much more frequently MSI and show a more favorable prognosis, likely related to their high density of TILs, which have independent prognostic value in SBC. MSI status, KRAS/NRAS mutations and HER2 amplifications might contribute to stratify patients for targeted anti-cancer therapy.

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