SO02: DNA mismatch repair genes deficiency is a frequent phenomenon in small intestine adenocarcinoma

Ariadna Sanchez1, Sabela Carballal1, Miriam Cuatrecasas2, Teresa Ocana1, Maria Pellisé1, Maria Liz Leoz1, Antoni Castells1,Francesc Balaguer1,Leticia Moreira1.

1 – Department of Gastroenterology, Hospital Clínic of Barcelona, Centro de Investigación Biomédica en Red en Enfermedades Hepáticas y Digestivas (CIBEREHD), IDIBAPS, University of Barcelona, Barcelona, Catalonia, Spain. 2 – Department of  Pathology ,Hospital Clínic of Barcelona, IDIBAPS, University of Barcelona, Barcelona, Catalonia, Spain.

Aim

Etiological and molecular mechanisms had been poorly described in small intestine adenocarcinoma(SIA). Our aim is to describe the clinic-pathological characteristics of SIA, and assess the role of  DNA mismatch repair (MMR) genes deficiency in these tumours.

Method

Retrospective, descriptive study including all (21) SIA diagnosed in our center between 2004-2014.  Personal, tumour-related, and family characteristics, as well as tumour MMR immunohistochemistry (IHC), and germline MMR mutational status data were reviewed.

Results

Eleven(52.4%) men, with a median age of 67(23-93) years. Median follow-up was 23.7(IQR 8.5-59.6) months with an overall 5-y-survival of 45.8%.  Ten(47.6%) tumours were located in duodenum, 9(42.9%) in jejunum and 2(9.5%) in ileum. Twelve(57.1%) were diagnosed in advanced stages(III-IV) and 7(33.3%) had a high histological grade. IHC revealed pathological findings in 4(19%) tumours: 2(50%) with loss of expression in MLH1/PMS2 and 2(50%) in MSH2/MSH6. These patients were younger and had better survival, without statistically significant differences[age: 53.5(+12) vs 65(+17.5) years, p = 0.2; mortality: 25%vs 53%, p = 0.3]. Lynch syndrome was diagnosed in 2(50%) patients. No other hereditary syndromes were detected.

Conclusion

20% of SIA present MMR deficiency. Only half of the patients were diagnosed with Lynch syndrome. These results may suggest that, as described recently in colorectal cancer, somatic inactivation of MMR genes could explain these phenomena.

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