153 A rare case of ATTR amyloidosis mimicking malignant gastrointestinal tumor

Introduction/Objective Amyloidosis is characterized by the extracellular deposition of misfolded, insoluble fibrils that disrupt tissue structure and function. The most affected organs include the kidneys, heart, nerves, liver, and spleen. The most common forms include immunoglobulin light chain (AL), reactive (AA), and dialysis-related (β2-microglobulin) amyloidosis. Transthyretin-related (ATTR) amyloidosis is less frequent. Gastrointestinal (GI) involvement is rare, comprising a small fraction of cases confirmed by biopsy. GI amyloidosis usually presents with nonspecific symptoms such as weight loss, bleeding, and abdominal pain. Imaging often reveals colonic wall thickening and luminal narrowing; rarely, it appears as a mass mimicking a gastrointestinal tumor. Here, we present a case of ATTR amyloidosis manifesting as a mass lesion with liver metastasis-like features. Methods/Case Report An 87-year-old woman without prior history of amyloidosis presented with bright red gastrointestinal bleeding and abdominal pain. CT imaging revealed a large, circumferential mass in the ascending colon, mural thickening in the rectum, and hypodense liver lesions suggestive of metastasis. Colonoscopy identified a fungating, ulcerated, non-traversable mass in the ascending colon. Biopsy was inconclusive due to superficial sampling, raising suspicion for gastrointestinal malignancy. A right hemicolectomy with liver biopsy was performed, revealing a 3.4 × 3.1 cm ulcerated cecal lesion. Histology showed a tubular adenoma and extensive amyloid deposition in the intestinal wall and vasculature wall. Congo red and Thioflavin T staining confirmed amyloidosis, while kappa/lambda immunohistochemistry was noncontributory. Liver biopsy of the presumed metastatic lesions revealed amyloid nodules. LC-MS/MS analysis identified transthyretin-type (ATTR) amyloid with a ­Val142Ile variant. Genetic testing confirmed a heterozygous ­pathogenic TTR mutation (c.424G>A; p.Val142Ile) with autosomal dominant inheritance. Cardiac evaluation was normal, and nerve biopsy was negative for amyloid. A final diagnosis of systemic ATTR amyloidosis involving the liver and gastrointestinal tract was established. Further workup revealed additional amyloid deposits in the stomach and duodenum, as well as a WHO grade 2 well-differentiated neuroendocrine tumor in the duodenum. Results NA Conclusion In conclusion, we report a rare case of hereditary ATTRv amyloidosis involving the liver and gastrointestinal tract, clinically mimicking primary colon cancer with liver metastases. This case underscores the importance of recognizing atypical presentations of amyloidosis and highlights the need to consider as differential diagnosis of gastrointestinal tumors. It serves as a valuable educational example of colonic cancer mimickers.