[712] Utility of Sessile Serrated Adenoma as a Marker of Metachronous Colorectal Carcinoma

Mahin Mohammadi, Mads Carstensen, Michael H Kristensen, Hans J Nielsen, Susanne Holck. Hospital South, Naestved, Denmark; Hvidovre Hospital, Hvidovre, Denmark

Background: Identification of cancer precursors facilitates early detection of lesions with high risk of cancer. It is is well-established for conventional adenomas. The clinical significance of the sessile serrated adenoma (SSA) as a marker of metachronous colorectal carcinoma (MCRC) remains elusive, despite mounting evidence implicating the SSA as a significant player in the serrated carcinogenesis. The risk of MCRC (CRC detected more than 12 months after the index intervention) in non-dysplastic SSA is here evaluated.
Design: The base-line material comprised 219 SSAs, identified among 8.834 colorectal polyps originally coded as hyperplastic polyp (HP), as described previously [Mohammadi et al Pathol Res Pract 2011;207:410]. Out-come information within 17 months to 10 years of the index intervention was searched through pathology databases.
Results: During the follow-up period, 3 patients with SSA, all males, aged 45, 56, and 67 years, were diagnosed with MCRC, 1.5, 2, and 10 years, respectively. Further details on index polyp and MCRC are given in table 1.

Table 1.

Index polyp				MCRC
	Mut. Status	Site	Size mm	Histologic type	Mut. Status	MLH1 protein	Site
1.	Braf-WT	Rectum	3	Glandular	NP	Retained	Rectum
2.	Braf-mut.	Asc.* Sigm.*	9	Glandular	Braf- and Kras WT	Retained	Rectum
3.	Braf-WT	Rectum	11	Mucinous	Kras-mut (12 wasp)	Retained	Left colon

Mut.: mutation; NP: not performed (insufficient material); Asc.: ascending colon; Sigm.: sigmoid colon; *two synchronous SSAs; WT: wild type.


Conclusions: The three examples of CRC identified were considered MCRC rather than lesions missed on the index endoscopy. Thus, index colonoscopy was performed under optimal conditions and the anatomic regions with CRC were all well visualized. Merely 1.4% of our study cases developed MCRC. This low figure was unexpected considering the following two facts: 1) the polyps were initially diagnosed as HP, implying that control surveillance was generally not offered, 2) the inconspicuous, sessile quality of SSA increases the risk of incomplete sampling. Apparently, such putative SSA-remnants were not prone to progress to MCRC, perhaps due to absence of dysplasia. Neither large size nor proximal site of the index polyp was consistent features of the MCRC cases. Of further note is the lack of convincing markers of a methylator pathway as might be anticipated if the index polyps played a role in the CRC development. Given the small sample size of this analysis, these observations need, however, to be addressed in additional large-scale studies prior to defining appropriate management strategies for this group of patients.
Category: Gastrointestinal

Tuesday, March 20, 2012 1:00 PM

Poster Session IV # 77, Tuesday Afternoon