Diagnostic challenge in distinguishing intestinal endometriosis-associated carcinoma from primary colorectal adenocarcinoma: a case report

Achoimre

Abstract Malignant transformation of intestinal endometriosis is rare and may closely mimic primary colorectal adenocarcinoma. A 43-year-old woman with a history of ovarian endometriosis presented with melena and a rectosigmoid tumor with uterine invasion and multiple lymph node metastases. Histopathological examination revealed moderately differentiated adenocarcinoma with intestinal endometriosis but no definitive transition between the endometriosis and the carcinoma, supporting an initial diagnosis of primary colorectal adenocarcinoma. Five years later, biopsy of a recurrent vaginal stump lesion showed an adenocarcinoma positive for estrogen receptor, paired box gene 8, and cytokeratin 7 and negative for cytokeratin 20 and caudal-type homeobox transcription factor 2. Retrospective immunohistochemical evaluation of the original tumor demonstrated a similar phenotype, supporting a Müllerian origin and malignant transformation of intestinal endometriosis. This case illustrates the difficulty of determining tumor origin based on morphology alone and highlights the diagnostic value of immunohistochemistry.