Abstract 5252: In colorectal cancer (CRC), neuroendocrine carcinoma (NEC) is contaminated in the cancer given a confirmed diagnosis of poorly differentiated adenocarcinoma (P-ad-ca)

Abstract

Abstract Background: Most of CRC were well or moderately differentiated adenocarcinoma and P-ad-ca is very rare. In Japan, P-ad-ca was reported to be only 4-6% of all CRC. NEC is also rare. The incidence of that were reported to be less than 1%. One of their points of common is morphological poorly differentiated appearance. In this study, we evaluated the incidence of NEC contaminated in the CRC given a confirmed diagnosis as P-ad-ca. Material and Method: From 2009 to 2019, 816 CRCs were resected in department of Yokohama City University Hospital and 74 cases showing P-ad-ca or having a small region of P-ad-ca with well or moderately differentiated ad-ca (W-ad-ca, M-ad-ca). Among the 74 cases, there were 8 of P-ad-ca, 4 of W-ad-ca with P-ad-ca, 44 of M-ad-ca with P-ad-ca, and 18 W-ad-ca and M-ad-ca with P-ad-ca. Immunohistochemistry (IHC) using neuroendocrine markers (NM) including chromogranin A, synaptophysin and insulinoma-associated protein 1 (INSM1) was performed to identified NEC. Recently, a high incidence of Rb protein loss was reported in NEC of several organs, then IHC using Rb monoclonal antibody was also performed. The cancers showing immunohistochemically positive of at least one of the three NM and negative of Rb were identified as true NEC in this study. Results: At least one of the three NM was positive in the 39 cases. In these 39 cases, 3 cases were also Rb negative. Two of the three cases were region of P-ad-ca. These 2 P-ad-ca regions showed positive of NM. Interestingly, in the other one case, region of W-ad-ca showed positive of NM and negative of Rb. Region of P-ad-ca of the case showed positive of all three NM and Rb. From morphological appearance, this case was quite unlikely to true NEC. Conclusion: In 74 P-ad-ca, 2 cases might be true NEC in our small evaluation. NEC might be contaminated in the P-ad-ca of CRC which is difficult to be distinguished by only pathological findings of HE staining. Citation Format: Yuhan Rong, Yuma Takeda, Naoki Okubo, Akihiro Suzuki, Motohiko Tokuhisa, Noritoshi Kobayashi, Atsushi Ishibe, Ikuma Kato, Shoji Yamanaka, Satoshi Fujii, Itaru Endo, Yasushi Ichikawa. In colorectal cancer (CRC), neuroendocrine carcinoma (NEC) is contaminated in the cancer given a confirmed diagnosis of poorly differentiated adenocarcinoma (P-ad-ca) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5252.