221 Low Grade Neuroendocrine Tumor (Carcinoid) of the Interventricular Septum of the Heart

Introduction/Objective Cardiac tumors are rare, with myxomas being the most common primary cardiac tumor. Low-grade neuroendocrine tumors (NETs) are neoplasms arising from neuroendocrine cells, and they are most frequently found in the gastrointestinal tract and lungs. Historically, they were referred to as “carcinoid” tumors. NETs are relatively rare, with an estimated incidence ranging from 2.5 to 5 cases per 100,000 population per year. Involvement of the heart by NETs is exceedingly rare and almost universally represents metastasis from a distant primary. Cardiac metastasis from carcinoid tumors occurs in approximately 4% of patients, many of which have advanced disease and carcinoid syndrome. Primary neuroendocrine tumors of the heart are even rarer, with limited cases described in the literature, and their occurrence within the interventricular septum is virtually unknown. This report highlights a unique case of a low-grade neuroendocrine tumor presenting as a cardiac mass, with a unique natural history. Methods/Case Report A 56-year-old woman with a history of mitral valve minimally invasive surgical repair in 2015 presented with new-onset dyspnea on exertion, dizziness, and a recent presyncopal episode, but no chest pain, orthopnea, flushing, diarrhea, or lower extremity edema. Transthoracic echocardiography revealed a 4 cm spherical mass (size 4 cm) attached to the apex of the interventricular septum, protruding into the right ventricle. Cardiac CT angiography confirmed a well circumscribed mass with no invasion. Whole-body PET-CT showed increased radiotracer uptake localized to the cardiac mass, with no evidence of abnormal uptake elsewhere in the body. The initial impression was a cardiac myxoma. Surgical resection was performed. Gross examination revealed a rounded firm, tan yellow mass measuring 4.0 cm. Histologically, the tumor consisted of a neuroendocrine tumor composed of uniform cells with low-grade features, with no mitotic activity or necrosis. Immunohistochemical stains were positive for Pancytokeratin (AE1/AE3), Chromogranin, and Synaptophysin, supporting the diagnosis of a neuroendocrine tumor. The Ki-67 proliferation index was approximately 1%, indicative of a low-grade tumor. Immunohistochemical stains for Cytokeratin 7, Cytokeratin 20, TTF-1, PAX8, and GATA3 were negative. Of note, immunohistochemical stain for CDX2 was diffusely positive, strongly suggesting origin from a primary tumor in the midgut. Results NA Conclusion Neuroendocrine tumors of the heart are exceedingly rare and often present with non-specific symptoms or no symptoms at all. Imaging findings may mimic more common cardiac tumors, such as myxomas. Histopathologic evaluation and immunohistochemical profiling are essential for definitive diagnosis. CDX2 positivity by immunohistochemistry within metastatic carcinoid tumors is strongly associated with a small intestinal primary, even in the absence of a detectable primary lesion. This case demonstrates the necessity of considering alternate diagnoses other than myxoma for tumors in the ventricle. It also highlights the unique natural history of some of these lesions that present as metastases before detection of a primary tumor, and without the clinical features of carcinoid syndrome.