Endometriosis‑associated adenocarcinoma of the rectum is rare and is usually misdiagnosed as colorectal carcinoma or other gynecological tumors. In the current report, the clinicopathological features of endometriosis‑associated adenocarcinoma of the rectum in 2 patients were retrospectively analyzed and a literature review regarding this rare malignancy is presented. Case 1, a 49‑year‑old postmenopausal female patient, was admitted to Hubei Cancer Hospital, Tongji Medical College, Huazhong University of Science and Technology (Wuhan, China) due to a pelvic mass. Pelvic MRI revealed a 4.5x3.7‑cm mass in the rectal wall, which severely adhered to the uterine wall. Microscopically, moderately differentiated glandular adenocarcinoma diffusely extended throughout all intestinal wall layers. Adenomyosis was found in the uterine body adherent to the rectum. Case 2, a 38‑year‑old reproductive female patient, presented with hematochezia. Histopathology of the resected tumor demonstrated benign endometriosis foci and atypical hyperplasia glands contiguous with endometrioid carcinoma invading the intestinal wall, and no other primary tumor sites were found, which satisfied the criteria for the diagnosis of malignant transformation of endometriosis of the rectum. Immunohistochemical (IHC) staining of both tumors revealed a Müllerian origin but not an intestinal origin. Furthermore, next‑generation sequencing detected mutations of the BRCA1 (c.329dup), KRAS (c.35G>T), PIK3CA (c.3140A>G) and PTEN (c.750_751del) genes, and that microsatellite instability was high in case 1. In conclusion, endometriosis‑associated adenocarcinoma of the rectum is a rare malignant tumor that should be distinguished from colorectal carcinoma for optimal treatment. Surgery and pathologic examination with IHC staining, even with molecular analysis, are essential for the final diagnosis. Primary cytoreductive surgery with resection of all macroscopic detectable lesions should be performed whenever possible. More prospective, multicenter, large‑scale trials are required to examine the regimens and therapeutic value of adjuvant chemotherapy or radiology.

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