SAT-102 The Role of BRAF Testing of Rathke’s Cleft Cysts to Identify Missed Papillary Craniopharyngioma

Abstract Disclosure: E. Mignone: None. N.G. Candy: None. K. Barbara: None. I. Chapman: None. D.J. Torpy: None. S. Santoreneos: None. S.M. De Sousa: None. Aim The differential diagnosis of cystic sellar/suprasellar lesions include Rathke’s cleft cyst (RCC) and craniopharyngioma (CP). The papillary subtype (pCP) can be difficult to differentiate from RCC due to similar radiological and histological features, but the distinction is vital as RCC are non-neoplastic lesions readily curable by marsupialisation/subtotal resection, whereas CP is a locally invasive neoplasm requiring definitive management.We aimed to determine whether routine BRAF testing of RCCs might reveal missed pCP, noting that the BRAF V600E variant is detectable in ∼95% of pCPs. Method We undertook a retrospective cohort study of all RCCs resected by two pituitary neurosurgeons (SS and NV) over 2001-2023. In cases with sufficient operative specimens, we performed BRAF V600E immunohistochemistry (IHC) using paraffin sections and BRAF next generation sequencing (NGS) using extracted tumour DNA. Results Eleven patients had suitable specimens. BRAF IHC was performed in all eleven cases. BRAF NGS was undertaken in eight cases, with insufficient tissue in the remaining three cases.A single case had a diagnosis of RCC revised to pCP through BRAF testing (9%), with equivocal epithelial BRAF IHC staining and confirmation of the V600E variant by NGS. Another patient had positive epithelial BRAF IHC but was negative by NGS. Separate to the epithelial findings, all cases unexpectedly exhibited BRAF V600E IHC positivity in adjacent anterior pituitary tissue. Conclusion BRAF testing has the potential to accurately differentiate the diagnosis of RCC from pCP, with substantial prognostic and therapeutic implications. This finding is especially timely given the emerging paradigm shift to BRAF inhibitors instead of surgical management of pCPs. We accordingly recommend consideration of BRAF testing in RCCs, noting that BRAF V600E staining in anterior pituitary tissue appears to be a normal finding that should not be mistaken for neoplasia. Presentation: Saturday, July 12, 2025