eP120 - Rectal Adenocarcinoma with Concomitant Mediastinal Carcinoid Tumor

Purpose/Background: Rectal cancer is the second most common cancer of the large intestine. Often, neoadjuvant therapy can be administered to shrink locally advanced tumors prior to a surgical approach. These malignancies can metastasize to the liver, lungs, and peritoneum. It's an unusual event to have a rectal malignancy present alongside neuroendocrine malignancy from a different embryological origin. The presence of a rectal adenocarcinoma with a coexisting neuroendocrine tumor of the thymus has not been documented in the literature. Primary neuroendocrine tumors of the thymus, are highly aggressive and have a poor prognosis.Methods/Interventions: A case report of a Rectal Adenocarcinoma that presented with a concomitant Medistinal carcinoid tumor.Results/Outcomes: A 61-year-old Chinese woman presented to the emergency department with a one-week history of abdominal pain radiating to the back accompanied by a painless bloody bowel movement and unintentional 35-pound weight loss in two years. On evaluation, she was septic with a WBC of 21.5, fever, tachycardia, and hypotension.
A computed tomography (CT) scan of the abdomen and pelvis showed bowel wall thickening at the rectosigmoid junction and a pelvic collection measuring approximately 5.6 x 3.1 x 6.7 cm. She underwent CT-guided percutaneous drainage. A repeat CT scan showed an increased size of rectosigmoid abscess measuring 10.7 x 6.7 cm, not amendable to percutaneous drainage.

After patient stabilization on repeated rectal exam mild tenderness was noted, and a friable circumferential mass was palpable approximately 8 cm from the anal verge. A proctoscopy with biopsy and a diagnostic laparotomy were done. The proctosigmoidoscope could not be probed past the site of the nearly obstructing rectal lesion. A large abscess between the uterus and rectum on the right side was evacuated. Rectal biopsy showed a moderately-differentiated rectal adenocarcinoma. She was referred to oncology for chemotherapy.

Staging CT chest scan showed a mediastinal soft-tissue mass measuring 2.5 x 4.8 x 5.5 cm anterior to the ascending aorta and bilateral pleural effusion. The mass was excised via video-assisted thoracoscopic surgery. The pathology report concluded the mediastinal tumor to be a carcinoid tumor of the thymus with clean margins. Immunostain testing of the tumor specimen showed the cells to be positive for OSCAR keratin, chromogranin, and synaptophysin. The cells were negative for SOX-10, Melan-A, and S100 protein.Conclusion/

Discussion: While rectal adenocarcinoma metastasizing to the thymus does occur, the presence of a rectal adenocarcinoma with a concomitant thymic neuroendocrine tumor (TNT), is extremely rare, with a few more than 200 cases reported.
TNTs constitute less than 5% of all anterior mediastinal masses. A review of 157 cases indicated a male preponderance, a mean age of 54. They can be found incidentally on imaging. Typical tumors are generally low-grade and slow-growing, while atypical tumors are of a higher grade and grow rapidly. Almost 50% of TNTs are functionally active and are associated with endocrinopathies Markers, chromogranin, Leu-7, bombesin, neuron-specific enolase, cytokeratin, and synaptophysin aid in diagnosis; Melanocyte, serotonin, somatostatin, cholecystokinin, neurotensin, S100 protein, and metenkephalin may be present. Nearly all cases of TNTs are reactive for cytokeratins. In our case, tumor cells were atypical and stained positive for OSCAR keratin, chromogranin, and synaptophysin. Surgical resection of TNTs remains the gold standard of therapy.