Table of Contents Author Guidelines Submit a Manuscript
Case Reports in Pathology
Volume 2017, Article ID 3427343, 5 pages
https://doi.org/10.1155/2017/3427343
Case Report

Gastric Medullary Carcinoma with Sporadic Mismatch Repair Deficiency and a TP53 R273C Mutation: An Unusual Case with Wild-Type BRAF

1Department of Pathology, University of California, San Diego, 200 West Arbor Drive, MC 8320, San Diego, CA 92103, USA
2Department of Surgery, University of California, San Diego, 200 West Arbor Drive, MC 8320, San Diego, CA 92103, USA
3Department of Medicine, Division of Gastroenterology, University of California, San Diego, 200 West Arbor Drive, MC 8320, San Diego, CA 92103, USA

Correspondence should be addressed to Mark A. Valasek; ude.dscu@kesalavm

Received 12 April 2017; Accepted 5 July 2017; Published 3 August 2017

Academic Editor: Lubos Holubec

Copyright © 2017 Brett M. Lowenthal et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Medullary carcinoma has long been recognized as a subtype of colorectal cancer associated with microsatellite instability and Lynch syndrome. Gastric medullary carcinoma is a very rare neoplasm. We report a 67-year-old male who presented with a solitary gastric mass. Total gastrectomy revealed a well-demarcated, poorly differentiated carcinoma with an organoid growth pattern, pushing borders, and abundant peritumoral lymphocytic response. The prior cytology was cellular with immunohistochemical panel consistent with upper gastrointestinal/pancreaticobiliary origin. Overall, the histopathologic findings were consistent with gastric medullary carcinoma. A mismatch repair panel revealed a mismatch repair protein deficient tumor with loss of MLH1 and PMS2 expression. BRAF V600E immunostain (VE1) and BRAF molecular testing were negative, indicating a wild-type gene. Tumor sequencing of MLH1 demonstrated a wild-type gene, while our molecular panel identified TP53 c.817C>T (p.R273C) mutation. These findings were compatible with a sporadic tumor. Given that morphologically identical medullary tumors often occur in Lynch syndrome, it is possible that mismatch repair loss is an early event in sporadic tumors with p53 mutation being a late event. Despite having wild-type BRAF, this tumor is sporadic and unrelated to Lynch syndrome. This case report demonstrates that coordinate ancillary studies are needed to resolve sporadic versus hereditary rare tumors.