Metastatic large cell neuroendocrine carcinoma of the lung arising from the uterus: A pitfall in lung cancer diagnosis.

A 41-year-old female smoker presented with a vaginal mass. Gynecological examination showed a mass filling the uterine corpus, cervix, and vagina. A total abdominal hysterectomy was performed. Macroscopic findings included a large fragile mass involving the uterine cavity, cervix, and vagina. Histology revealed atypical ducts admixed with solid components consisting of large atypical cells. The initial pathological diagnosis was grade 3 endometrioid adenocarcinoma. The patient was designated as stage II according to the 2008 International Federation of Gynecology and Obstetrics (FIGO) staging. Two years later, two nodules were found in the upper lobe of the left lung, and the patient underwent an upper lobectomy. The masses, which exhibited solid and organoid growth patterns of large atypical cells, had histological characteristics of large cell neuroendocrine carcinoma (LCNEC) of the lung. However, the tumor was immunohistochemically positive for neuroendocrine markers, such as synaptophysin in addition to estrogen receptor and progesterone receptor, and the tumor was negative for thyroid transcription factor-1. These immunohistochemical results were almost identical to those of the solid portions of the uterine carcinoma. The final diagnosis was LCNEC combined with endometrioid adenocarcinoma of the uterine corpus and lung metastasis of the LCNEC component of the endometrial carcinoma. LCNEC often arises in the lung, but it rarely arises in other organs. Some patients with metastatic components exhibited only a LCNEC pattern although the primary tumor was a mixed carcinoma consisting of LCNEC and other histology, like the present case. LCNEC is often poorly differentiated, especially in extrapulmonary primary organ LCNEC. Therefore, pathologists should consider metastatic carcinoma when they encounter lung LCNEC in a patient with a preceding extrapulmonary carcinoma composed of a poorly differentiated component or LCNEC component, and they should clarify tumor immunohistochemical characteristics to confirm the diagnosis.