**Author Listing - Lead/ Submitting Author (we will be communicating with this individual): Name, Institution, City and State where the work was done. Co-authors will be added in a separate section.**
Catherine E. Hagen, Mayo Clinic, Deparment of Laboratory Medicine and Pathology, Rochester, MN, USA

**Main Body of the Abstract**
Background: Amyloidosis involving the gallbladder is rare and few studies have evaluated it systematically.
Objective: To determine the clinical, morphologic, and proteomic features of amyloid in cholecystectomy specimens.
Material & Methods: Congo Red positive cholecystectomy specimens (N=118) were identified. Detected amyloid deposits were analyzed using a clinical proteomics-based amyloid typing assay at Mayo Clinic. A pathologist scrutinized each amyloid proteomics profile and assigned a type based on the most abundant amyloidogenic protein. Clinical information was available for 10 patients. A feasible subset (N=26) underwent morphological analysis for localization of amyloid within the gallbladder wall.
Results: We detected the following amyloid types: N=63 ATTR (53.4%), N=46 AL (39.0%), N=4 AA (3.4%), N=2 AApoAI (1.7%), N=2 ALECT2 (1.7%), N=1 EFEMP1 (0.8%). We detected known amyloidogenic mutations (p.Val142Ile variant) in 3 ATTR cases (3/63, 4.8%). Clinical information is summarized in Table 1. In the majority (70%), amyloid was an unexpected diagnosis first made on the cholecystectomy specimen. In 2 additional patients, cholecystectomy was performed prior to amyloid diagnosis but amyloid involvement was initially missed; following a diagnosis of cardiac amyloidosis, gallbladder amyloid involvement was retrospectively identified. Morphological analysis revealed all cases (n=26) had amyloid deposition within perimuscular vessels.
Summary & Conclusion: We identified 6 different types of amyloid involving cholecystectomy specimens, with AL and ATTR types accounting for 92.4%. The gallbladder may often be the first site of amyloid diagnosis. Careful evaluation of cholecystectomy specimens, in particular assessment of perimuscular vessels, can prevent delay in diagnosis of systemic amyloidosis.



Gallbladder Amyloid is Often Unexpected and May Have Systemic Implications PA91 (#88)

We invite you to attend the XIX International Symposium on Amyloidosis to be held in Rochester, MN.

This symposium is organized as a hybrid meeting (with the focus on in-person) held from Sunday, May 26 through Thursday, May 30, 2024.

Together with the ISA Board and members of Mayo Clinic, a very attractive scientific hybrid program is being planned. The program will cover a variety of types of systemic amyloidosis: ATTR (hereditary and wild-type), AL (light-chain), AA and less frequent forms. There will be key lectures, specific symposia including those company sponsored, oral presentations and poster sessions of accepted abstracts.

COURSE DESCRIPTION
This program will provide a comprehensive review of state-of-the-art education in systemic amyloidosis: basic science, pathophysiology, diagnosis, current and emerging treatments. Scientific presentations will include competitive oral and poster abstracts. The rapid evolution of scientific discovery and expanding treatment options has created tremendous interest in the field and this meeting will fill and important gap in educating scientists and clinicians.