[613] Appendiceal Serrated Neoplasms Are More Frequently Associated with Right-Sided Than Left-Sided Colorectal Adenocarcinoma.

Jon M Davison, Alyssa M Krasinskas, Marina N Nikiforova, Shihfan Kuan. University of Pittsburgh, PA

Background: Serrated neoplasms are seen in the colon and appendix. Although significant difference exist, there are morphologic and molecular similarities between serrated neoplasms of the appendix and their colonic counterparts. Colonic sessile serrated adenomas (SSA) are thought to be a precursor of microsatellite unstable (MSI-H) colorectal cancer (CRC), both of which are more common in the right colon than the left colon which mainly habors micosatellite stable (MSS) CRCs. This study addresses the question of whether appendiceal serrated neoplasms are also more commonly found in association with right sided CRC than left-sided CRC and whether there is an association with the MSI status of the CRC.
Design: We studied 3 groups of colectomy specimens which included the appendix in the same operation:(1) right-sided MSI-H CRC (n=65), (2) right-sided MSS CRC (n=80), and (3) all left-sided CRC (n=120). Consensus diagnoses of appendiceal lesions were made by 3 GI pathologists. The microsatellite status was established by a panel of 5 NCI markers for all right-sided CRCs. MUC6, a marker for SSA was assessed by immunohistochemistry.
Results: Appendiceal epithelial lesions were seen in 15 of 265 CRCs with appendectomy. These included 8 serrated neoplasms: sessile serrated adenoma (SSA, n=4), and mixed serrated and adenomatous neoplasm (MSAN, n=4). Other lesions included conventional mucinous cystadenomas (MCA, n=4) and hyperplastic polyps (HP, n=3). All 8 appendiceal serrated neoplasms (SSA and MSAN) were associated with right-sided CRCs and none were encountered in appendectomies that accompanied left-sided CRC.

Table 1

	SSA or MSAN	MCA	HP
Right-sided CRCs (n=145)	8¶	2	2
Left-sided CRCs (n=120)	0¶	2	1

¶p=0.009, Fisher's exact test

Appendiceal serrated neoplasms (SSA and MSAN) were more frequently associated with MSI-H than MSS CRCs, though this result was not statistically significant.

Table 2

	SSA or MSAN	MCA	HP
Right-sided MSI-H CRCs (n=65)	6§	1	1
Right-sided MSS CRCs (n=80)	2§	1	1

§p=0.14, Fisher's exact test

All serrated neoplasms expressed MUC6. Four MCAs and 3 HPs of the appendix were negative for MUC6.
Conclusions: Appendiceal SSAs are commonly associated with right-sided CRCs with a trend toward an association with right-sided MSI-H CRCs. These associations are similar to those of colonic SSA. Our results suggest that there may be a common pathogenesis for colonic and appendiceal serrated neoplasms.
Category: Gastrointestinal

Wednesday, March 2, 2011 9:30 AM

Poster Session V # 31, Wednesday Morning