MON-080 - Unexpected Pathology: Primary Neuroendocrine Tumor of the Liver Presenting as A Suspected Breast Cancer Metastasis

Background:
Primary hepatic neuroendocrine tumors (PHNETs) are exceedingly rare and are most often misdiagnosed as metastatic disease due to the liver’s role as a common site of neuroendocrine tumor spread. Diagnostic uncertainty is amplified in patients with a prior history of malignancy, where new hepatic lesions are frequently attributed to recurrence. Accurate diagnosis requires careful histopathologic and immunohistochemical evaluation.

Case Presentation:
A 67-year-old woman with a history of hormone receptor–positive lobular breast carcinoma status post lumpectomy with adjuvant radiation therapy, ongoing anti-hormonal therapy, and bladder cancer status post resection presented with progressive systemic symptoms. She reported a 30-pound unintentional weight loss over three months, chronic diarrhea, night sweats, fatigue, and increasing abdominal fullness.

Computed tomography of the abdomen and pelvis revealed marked hepatomegaly with innumerable diffuse hepatic masses, initially presumed to represent metastatic breast cancer. Laboratory evaluation, including liver function tests and tumor markers, was unremarkable. Ultrasound-guided liver biopsy demonstrated a well-differentiated grade 2 neuroendocrine tumor. Immunohistochemical staining was positive for cytokeratin CAM5.2, synaptophysin, INSM1, and E-cadherin, with weak SATB2 positivity, and negative for cytokeratin 7 and cytokeratin 20, findings inconsistent with metastatic breast carcinoma.

DOTATATE PET/CT revealed multiple somatostatin receptor–avid hepatic lesions and peritoneal soft-tissue nodules, consistent with disseminated neuroendocrine tumor involvement. Chromogranin A and plasma metanephrines were within normal limits, suggesting a nonfunctional tumor. Extensive evaluation for an extrahepatic primary source, including CT chest imaging, esophagogastroduodenoscopy, and colonoscopy, was unrevealing.
Given diffuse hepatic involvement, the patient was not a candidate for surgical resection and was initiated on monthly lanreotide therapy, which she tolerated well.

Conclusion:
This case highlights the importance of maintaining a broad differential diagnosis when evaluating hepatic lesions in patients with a history of malignancy. PHNETs, though rare, should be considered when histopathology is inconsistent with metastatic disease. Tissue diagnosis and somatostatin receptor imaging are essential for accurate classification and appropriate endocrine-directed management.

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