Impact of histopathological revision and molecular pathology in the diagnosis of sarcomas in a reference center in Brazil

e23533 Background: The accurate classification of sarcomas remains a major challenge due to the diversity and rarity of this group of mesenchymal tumors. In addition to standard microscopy and immunohistochemical techniques, molecular analyses are often required to achieve an appropriate diagnosis. The limited availability of specialized pathology centers, multidisciplinary teams, and diagnostic tools may directly affect the initial evaluation and subsequent treatment plan. Therefore, we sought to characterize the impact of diagnostic review by reference pathologists and molecular assessments in a reference center in Brazil. Methods: We conducted a retrospective analysis of sarcoma samples initially analyzed at outside laboratories and subsequently revised in a reference center by two dedicated pathologists between 01/2014-12/2020. After extracting demographic and tumor characteristics, we assessed the presence of complete discordance (benign versus malignant, sarcoma versus other malignancy), partial concordance (similar diagnosis of connective tumor, but different grade/histological subtype/differentiation), and complete concordance. The concordance for histology or grade, as well as the role of molecular assessments supporting the diagnosis, were also independently determined. Statistical analyses were conducted through the kappa coefficient of agreement, adherence by χ2 test, χ2 test by Person, and Fisher's exact test. Results: A total of 197 cases were included, with a predominance of male patients (57.9%), localized tumors (86.8%), and the median age at diagnosis of 46.3 years. The most common primary sites were lower extremities (34.6%) and retroperitoneum (11.3%). Following the revision, the most frequent histologies were undifferentiated pleomorphic sarcoma (20.3%), liposarcomas (13.1%), and leiomyosarcoma (6.6%). Complete discordance was present in 13.2%, partial discordance in 45.2%, and complete concordance in 41.6% of reviews (p < 0.001). We found a concordance for histology or grade of 53.5% (p < 0.001) and 51.8% (p < 0.001) respectively. Molecular assessments, comprising NGS panels (79.5%) and FISH (20.5%), were performed in 44 (22.3%) cases, with findings of diagnostic relevance in 31.8% of those. Conclusions: In almost 60% of the cases, the initial diagnosis was at least partially modified when revised in a reference center, with a relevant impact of molecular assessments. These findings highlight the importance of managing sarcoma patients in reference centers and justify the assembly of referral networks in countries with limited healthcare resources.