Sa1144 Clinical Impact of Endoscopic Ultrasonography for Small Diameter Rectal Neuroendocrine Tumors

as PDNET, and 7 PDNEC based on morphologic features. WDNETs had low-grade cytology and mitotic figures less than 20 per 10 high-power fields. PDNECs demonstrated high grade cytology, sheet-like growth, and higher mitotic activity. PDNETs had intermediate features. Ki-67, p53, and p16 expression data are shown in Table 1. P53 expression in less than 30% of the tumor was considered negative. Conclusion: Tumors with morphologic features of well-differentiated neuroendocrine tumors do not express p53 and rarely express p16. Poorly-differentiated neuroendocrine tumors exhibit Ki-67 indices between 15-40%, with intermediate expression of p53 and p16. Poorly-differentiated neuroendocrine carcinoma with Ki-67 expression greater than 40% had the highest levels of p53 and p16 expression and the worst survival from the time of diagnosis. These data support the hypothesis that patients with neuroendocrine neoplasms of the gastrointestinal tract currently classified as grade 3 (neuroendocrine carcinoma) have variable survival. Further stratification of these patients based on proliferative indices may better predict clinical behavior, and further investigation with larger cohorts is warranted. Moreover, these data suggest expression of p53 and p16 by immunohistochemistry correlate with increasing grade and worse survival, and these markers may be useful in stratifying patients. Table 1