Gastric endocrine cell hyperplasia after neoadjuvant therapy for poorly cohesive carcinoma: a diagnostic pitfall

Abstract

Mucosal endocrine cell hyperplasia is a poorly described phenomenon that may occur following neoadjuvant therapy in a variety of gastrointestinal cancers. We describe two cases of poorly cohesive gastric carcinoma which underwent neoadjuvant chemotherapy. Subsequent biopsy and resection showed the presence of endocrine cells occurring singly and in micronests within the deep lamina propria, showing typical reactivity with synaptophysin and chromogranin. The distribution of these cells and cytokeratin positivity may mimic residual poorly cohesive carcinoma, particularly in small post-therapy biopsies. This phenomenon is thought to be related to normal mucosal elements being rendered relatively conspicuous by the depletion of malignant cells in cases with good neoadjuvant response. This treacherous finding may be misdiagnosed on small biopsies as residual malignancy, leading to potentially avoidable differences in subsequent management. This error may be avoided by awareness of this phenomenon and applying a simple panel of directed immunohistochemical markers, coupled with morphological correlation. Endocrine cell hyperplasia post neoadjuvant therapy in poorly cohesive carcinoma is a mimic of residual disease and may be result in false-positive interpretation of residual disease. Interpretation of post-treatment small biopsies should take into account this finding to avoid this potential clinically significant diagnostic pitfall.