EC is the fourth most common type of cancer among women, and its mortality rate has risen over the past 20 years [1]. Endometrioid carcinoma is the most prevalent histological type, while serous endometrial carcinoma, which comprises 5–10% of all EC cases [2], carries a poorer prognosis, with a 5-year survival rate between 60 and 65% [3]. EC metastasis primarily occurs in the vagina (42%), lungs (27%), and peritoneum (27%) [1]. Metastasis to the colon is extremely rare and is most often attributed to direct spread or peritoneal dissemination. In addition, it has been suggested that EC can also disseminate transovarially, even in the early stages [4]. Atypical metastatic sites for EC, such as those associated with a history of endometriosis, have been reported [5]. However, in the current case, there is no history of endometriosis or symptoms suggesting such a condition. While the prognosis in the early stages is generally favorable, with infrequent local or distant recurrences, metastases can manifest in various locations years after the initial treatment [6]. Risk factors for recurrence in early-stage EC include a histologic grade 3, age > 60 years, depth of myometrial invasion, lymph vascular invasion, and involvement of the lower uterus [7]. In this case, the patient’s age and lymph vascular invasion were significant risk factors.

Most colon carcinomas are primary tumors; however, secondary tumors can also be found. When comparing the frequency of primary sites for metastatic colon tumors, the stomach and ovaries are the most common, followed by the pancreas [8]. The uterine endometrium is considered a relatively rare primary site. Endometrial and colorectal carcinomas exhibit morphological similarities, often causing colon tumors to be mistaken for primary carcinomas. In the current case, a preoperative endoscopic biopsy indicated a diagnosis of colorectal carcinoma, leading to surgery under the suspicion of this diagnosis. However, distinct immunohistochemical profiles can differentiate between these cancers. It has been reported that 75–95% of carcinomas originating from the colonic mucosa are CK7 negative and CK20 positive, whereas 80–100% of carcinomas originating from endometriosis are CK7 positive and CK20 negative [9, 10]. Additionally, CDX2 is a potential marker for primary colorectal tumors, with most studies showing that CDX2 is a sensitive marker with a reported sensitivity of up to 90% [11]. In the current study, both CK7 and CK20 were negative, but CDX2 was also negative, and the histological diagnosis was serous carcinoma consistent with endometrial carcinoma tissue, leading to the diagnosis of EC metastasis. Metastatic forms include lymph vascular and disseminated, and it is difficult to conclude that this is metastasis to the colon rather than the invasion of peritoneal dissemination. The classification of gross appearance is often described as ulcer localized type in the lymph vascular form and ulcer invasion type in the disseminated form [12]. In the current case, the classification of gross appearance is ulcer localized type. In addition, the main site of tumor was not on the serosa, but on the submucosa and muscle layers which is common in the lymph vascular form [12]. Therefore, we thought this case was most likely metastasis to the colon rather than the invasion of peritoneal dissemination.

Colorectal metastases, similar to primary colorectal carcinoma, are often detected through symptoms such as abdominal pain or bleeding. In the present case, the patient presented with abdominal pain and intestinal obstruction. However, there is only one previously reported case where the patient presented with intestinal obstruction due to colorectal metastasis [13]. For the treatment of EC metastasis, tumor resection or tumor reduction surgery is recommended [14]. Given the patient’s bowel obstruction, a stent was inserted preoperatively, followed by a standby operation. To the best of our knowledge, this is the first reported case of bowel obstruction due to EC metastasis where a stent was inserted, and the patient was operated on standby. Postoperative chemotherapy options include doxorubicin + cisplatin or paclitaxel + carboplatin therapy. In this case, chemotherapy was not selected, considering the patient’s preference.

There have been 9 [6,7,8,9, 13, 15,16,17,18] reported cases of colonic metastasis of EC, with 10 cases, including ours, listed in Table 1. Endometrioid carcinoma was the most common type, with only two cases being serous carcinoma, like the present case. The stages at initial surgery were Stage I in 5 cases, Stage II in 1 case, Stage III in 2 cases, and 2 cases with uncertain staging. This indicates that colon metastasis can occur even at an early stage. Additionally, there is a wide range in the interval between the first surgery and recurrence (0.1–15 years), with the longest interval being 15 years, suggesting that recurrence may occur several years later. Preoperative diagnosis of colon metastasis of EC was possible in 5 cases, while 4 cases, including ours, were initially diagnosed as primary colon tumors. Therefore, clinicians must consider the possibility of metastatic disease, especially if there is a history of EC. Furthermore, follow-up is crucial because recurrence can occur several years later, even in early-stage cancer.