Value of SATB2 immunostaining in the distinction between small intestinal and colorectal adenocarcinomas

Aims Special AT-rich sequence-binding protein 2 (SATB2) is a novel immunomarker that is expressed in glandular cells of the lower gastrointestinal tract with retained expression in the majority of primary and metastatic colorectal adenocarcinomas (CRCs). Because of its tissue specificity, SATB2 has been shown to be a clinically useful marker to distinguish CRC from non-CRC. In this study, we investigated whether or not SATB2 can help differentiate CRC from small intestinal adenocarcinoma (SIA), a practical diagnostic challenge due to their morphological and immunophenotypic similarities. Methods Fifty surgically resected primary SIAs and 50 CRCs were immunohistochemically examined for the expression of SATB2. Positive staining was graded as 1+ (5-25% of the tumour cells stained), 2+ (26-50%), 3+ (51-75%) or 4+ (>75%), as well as weak, intermediate or strong for staining intensity. Results Positive SATB2 immunoreactivity was observed in 23 (46%) SIAs in contrast to 48 (96%) CRCs (p<0.0001). Among these, only 4 (8%) SIAs showed strong and diffuse (4+) SATB2 staining compared with 38 (76%) of CRCs (p<0.0001). Conclusions SATB2 is not entirely CRC-specific and is expressed in a subset of SIAs. Unlike CRC, however, SIA infrequently shows a strong and diffuse staining pattern, which still makes SATB2 a useful immunomarker to distinguish SIA from CRC.