P2806 - Metastatic Mixed Adenoneuroendocrine Carcinoma Presenting as a Poorly Differentiated Sarcomatoid Neoplasm

Nichole C.. Henkes, MD¹, David Henkes, MD^2
1Mayo Clinic Florida, Jacksonville, FL; ²Christus Santa Rosa Medical Center, San Antonio, TX

Introduction: Mixed adenoneuroendocrine carcinoma (MANEC) of the gastrointestinal tract is an unusual tumor composed of adenocarcinoma mixed with a neuroendocrine component, each comprising at least 30% of the tumor. We report a case of a primary gastric MANEC that metastasized to the liver and underwent dedifferentiation to a more primitive cell lineage.

Case Description/Methods: A 76-year-old male with end stage renal disease status post renal transplant on immunosuppressives presented to the hospital with 2-3 weeks of decreased appetite, vomiting and poor oral intake. Imaging of the abdomen revealed liver lesions suggestive of metastatic disease or lymphoma. Liver core biopsy revealed positive immunostains and histology most consistent with poorly differentiated angiosarcoma of liver origin.

Two months later, repeat imaging showed significantly increased liver tumor burden and a gastric antral mass was discovered. Biopsy of the gastric mass revealed an invasive adenocarcinoma in a background of high-grade dysplasia. Further characterization revealed individually staining components of adenocarcinoma along with neuroendocrine tissue. These findings supported the diagnosis of a gastric MANEC.

Reexamination of the liver tumor showed focal areas (< 5%) where the tumor had histologic features similar to the neuroendocrine component of the gastric tumor and no adenocarcinomatous areas were present.

Discussion: The biological behavior of MANEC seems to be unpredictable and the prognosis uncertain. Although some studies suggest metastasis of MANEC tumors, the literature is limited in the description of histology of the metastatic lesions. One case report documents a gastric MANEC tumor with tri-lineage differentiation with only neuroendocrine expression in a liver metastasis. Our case had traditional MANEC elements of glandular and neuroendocrine in the primary gastric tumor but evidence of dedifferentiation with sarcomatous features in the metastatic tumor.

The patient’s gastric and liver tumors rapidly increased in size, indicating an aggressive disease and was deemed incurable. From initial presentation to time of death, less than 6 months had passed. Due to its rarity and limited literature available, it is uncertain whether this poor prognosis is characteristic of MANEC tumors or if it is an outlier. One may speculate whether the metastatic dedifferentiation is associated with immunosuppressive therapy or is a feature seen in highly aggressive MANEC tumors.


Disclosures:


Nichole C.. Henkes, MD¹, David Henkes, MD². P2806 - Metastatic Mixed Adenoneuroendocrine Carcinoma Presenting as a Poorly Differentiated Sarcomatoid Neoplasm, ACG 2023 Annual Scientific Meeting Abstracts. Vancouver, BC, Canada: American College of Gastroenterology.