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Objectives Flat epithelial atypia (FEA) is a relatively new diagnostic term with uncertain clinical significance for surgical management. Any implied risk of invasive breast cancer associated with FEA is contingent upon diagnostic reproducibility, yet little is known regarding its use. Materials and Methods Pathologists in the Breast Pathology Study interpreted one of four 60-case test sets, one slide per case, constructed from 240 breast biopsy specimens. An electronic data form with standardized diagnostic categories was used; participants were instructed to indicate all diagnoses present. We assessed participants’ use of FEA as a diagnostic term within: 1) each test set; 2) 72 cases classified by reference as benign without FEA; and 3) six cases classified by reference as FEA. 115 pathologists participated, providing 6,900 total independent assessments. Results Notation of FEA ranged from 0% to 35% of the cases interpreted, with most pathologists noting FEA on 4 or more test cases. At least one participant noted FEA in 34 of the 72 benign non-FEA cases. For the 6 reference FEA cases, participant agreement with the case reference FEA diagnosis ranged from 17% to 52%; diagnoses noted by participating pathologists for these FEA cases included columnar cell hyperplasia, usual ductal hyperplasia, atypical lobular hyperplasia, and atypical ductal hyperplasia. Conclusions We observed wide variation in the diagnosis of FEA among U.S. pathologists. This suggests that perceptions of diagnostic criteria and any implied risk associated with FEA may also vary. Surgical excision following a core biopsy diagnosis of FEA should be reconsidered and studied further.

7571 Background: Burkitt lymphoma (BL) is a rare, but highly aggressive B-cell lymphoma associated with especially poor outcomes in patients with relapsed/refractory disease. Multiple CD19 chimeric antigen receptor (CAR) T-cell products have been FDA approved to treat relapsed/refractory B-cell non-Hodgkin lymphoma in the second-line setting, however little is known about CAR T-cell responses in patients with BL. This multicenter study aims to assess real-world outcomes among patients with BL treated with CAR T-cell therapy across the United States. Methods: This multicenter, retrospective chart review was conducted by abstracting data from the medical charts of patients with BL who received CAR T-cell therapy. Demographic characteristics were assessed along with pre-CAR treatments, bridging therapies, infusion-related complications, CAR-T responses, and the use of post-CAR systemic therapy and/or hematopoietic stem cell transplant. Results: A total of 13 patients with relapsed/refractory BL received CAR T-cell therapy after a median of 3 prior therapies (range 1-6). Most patients received axi-cel (n = 8), although tisa-cel (n = 3) and liso-cel (n = 2) were also represented. The median age of these patients was 38 (range 24-68). A total of 6 (46.2%) had evidence of central nervous system involvement at diagnosis and 5 (38.5%) had a prior history of autologous stem cell transplant. The overall response rate 1 month after infusion was 69.2% with a complete response rate of 53.8%. All patients experienced grade 1-2 cytokine release syndrome (CRS). No one experienced grade ≥3 CRS, but 2 patients developed grade ≥3 immune effector cell-associated neurotoxicity syndrome (ICANS). Twenty-eight-day mortality was 23%, including one patient who died from grade 4 ICANS. Regarding long term data, only 4 (30.8%) patients sustained a complete response for more than 6 months. Median progression-free survival was 4.2 months (95% CI 28.2-257.6), and the 1-year overall survival rate was 61.5% (95% CI 0.56-0.67). Two (15.4%) patients received consolidative allogeneic stem cell transplants after CAR T-cell therapy, but both ultimately developed progressive disease. Conclusions: Relapsed/refractory BL is a rare and aggressive disease that remains challenging to treat despite the advent of CAR T-cell therapy. Further investigation is needed to determine the most effective management of these patients. We expect to include additional patients in this analysis over the coming months.

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