[664] Utility and Limitations of MUC6 Immunohistochemistry for the Diagnosis of Sessile Serrated Adenomas

N Shafizadeh, YY Chen, GE Kim, S Kakar. UCSF, San Francisco, CA

Background: Sessile serrated adenomas(SSA) are distinguished from typical hyperplastic polyps(HP) by abnormal maturation and/or proliferation. SSA may be precursor of microsatellite unstable colorectal cancer and hence warrant surveillance similar to adenomatous polyps. However,the morphological distinction of SSA from HP can be difficult. Aberrant expression of MUC6, a gastric type mucin, has been reported in SSA but not in other types of serrated polyps. This study evaluates the specificity of MUC6 expression for SSA and explores its utility for routine diagnostic use.
Design: 72 colorectal polyps were classified as HP, SSA, traditional serrated adenoma(TSA) and tubular adenoma(TA) by 3 experienced GI pathologists using previously published criteria. A consensus diagnosis was reached in the discrepant cases by collective review. The polyps with suggestive but not unequivocal features of SSA were designated as probable SSA. Immunohistochemistry for MUC6 was performed in all cases and scored as negative,focal positive (<5 crypts) and diffuse positive (>5 crypts).
Results: There was agreement in 58(81%) cases; a consensus diagnosis was established in the rest. There were 15 HP, 20 SSA, 10 probable SSA, 17 TSA and 10 TA. MUC6 expression was predominantly in the basal crypts and significantly more common in SSA compared to HP(p=0.02) and TSA(p<0.001). All SSA and probable SSA on the right side were MUC6+. Negative MUC6 was seen in 3 SSA and 2 probable SSA, all of which were located in the left colon. One SSA showed dysplasia; both the SSA and the dysplastic areas showed diffuse MUC6 expression. Diffuse staining was seen in 13(65%) SSA and 5(50%) probable SSA compared to 2(13%) HP and 2(12%) TSA.Of the 7 MUC6+ HP, 5(71%) were on the right, including both cases that were diffuse MUC6+.

	HP (n=15)	SSA (n=20)	Probable SSA (n=10)	TSA (n=17)	TA (n=10)
MUC6 +	7 (47%)	17 (85%)	8 (80%)	5 (29%)	1 (10%)
MUC6 diffuse +	2 (13%)	13 (65%)	5 (50%)	2 (12%)	1 (10%)

Conclusions: MUC6 expression has high sensitivity (>80%) for the diagnosis of SSA, and is positive in all right-sided cases. The staining is diffuse in majority of SSAs. Less often, MUC6 expression can be seen in HP and TSA, with focal staining in majority of cases. Diffuse staining can occur in approximately 10% of HP and TSA. Although not entirely specific, MUC6 immunohistochemistry can be useful for the diagnosis of SSA, especially if diffuse expression is obtained.
Category: Gastrointestinal

Wednesday, March 11, 2009 9:30 AM

Poster Session V # 80, Wednesday Morning