Small Cell Neuroendocrine Carcinoma of the Endometrium with Difficulty Identifying the Original Site in the Uterus

Diagnosis of malignant uterine tumor with continuous lesions from the uterine body to the cervix, i.e., endometrial or cervical cancer, depends on the main site of the lesions. However, it may be difficult to differentiate advanced cancer that is widespread in the uterus. We experienced a patient who was diagnosed with small cell neuroendocrine carcinoma (SCNEC) based on histopathological characteristics of SCNEC in the endometrium. This tumor frequently coexists with endometrioid carcinoma, but we had difficulty finding the original site of SCNEC in the endometrium. The patient was a 59-year-old, two-parous woman who underwent hysterectomy after diagnosis of malignant uterine tumor. Preoperative cervical and endometrial histology permitted diagnosis of SCNEC. Imaging showed that most of the anterior uterine wall from the uterine body to cervix was replaced by tumors. Histopathologic findings for the resected uterus showed that most of these tumors were SCNEC, but components of endometrioid carcinoma had developed from the endometrium just beneath the fundus to the lower uterine body. The growth pattern of endometrioid carcinoma was endophytic. Based on this finding, the patient was diagnosed with endometrial SCNEC associated with endometrioid carcinoma. The patient initially responded well after postoperative chemotherapy, but early recurrence led to death at three months after the first treatment. This case shows that SCNEC in the uterine body is likely to coexist with endometrioid carcinoma. These findings are useful to determine the original site in postoperative pathological diagnosis of highly advanced tumors. SCNEC is a rapidly progressive and aggressive tumor in clinical practice, but some cases have a relatively good initial response to chemotherapy and it is important to start treatment early.