**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.**
Name: Roberta Shcolnik Szor
Institution: Serviço de Hematologia, Hemoterapia e Terapia Celular, Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
City: Sao Paulo
Country: Brazil
Email: roberta.hemato@gmail.com

**Main Body of the Abstract**
Background: Systemic amyloidosis (SA) is often underdiagnosed and recognized late in middle-income countries. Limited access to specific tests makes the diagnostic journey a challenge. Precisely identifying the precursor protein is even more difficult, as mass spectrometry (MS) is not widely available. We aimed to retrospectively subtype amyloid by MS and evaluate the performance of a clinical-laboratory model (CLM) in amyloid typing.
Methods: Biopsies were randomly selected from a cohort of 143 patients diagnosed with SA from 2009 to 2020 at Hospital das Clínicas da Universidade de Sao Paulo, a Brazilian university hospital. Previous diagnoses and medical records were reviewed. CLM defined amyloid subtype by immunohistochemistry, indirect immunofluorescence or genetic mutation. When diagnostic criteria couldn´t be met, typing relied on available data and clinical judgment.
Results: Forty-nine biopsies were included from different organs (kidney 31%, heart 20%, subcutaneous fat 12%, gastrointestinal tract 10%, nerve 8%, lung 8%, lymph node, bone marrow, liver, salivary gland and tongue 2% each). MS identified the following subtypes: AL (57%, n=28), ATTR (25%, n=12), AA (6%, n=3) and AFib (2%, n=1).  Five cases were inconclusive due to poor quality of samples. The CLM correctly subtyped amyloid in 100% of AL, AA and AFib, and 75% of ATTR cases. Three patients with ATTR were misdiagnosed as AL, and one received anti-plasma cell agents.
Conclusion: Despite the good performance of CLM observed in our study, we emphasize the role of MS as the gold standard method to accurately subtype amyloid, avoiding potential harm from misdiagnosis and incorrect treatment.



Challenges in Amyloidosis Typing: The Role of Mass Spectrometry in a Middle-Income Country PA74 (#410)

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.