Targeted BRAF and CTNNB1 next-generation sequencing allows proper classification of nonadenomatous lesions of the sellar region in samples with limiting amounts of lesional cells

Purpose: To assess the role of high sensitivity next-generation sequencing (NGS) of CTNNB1 for the diagnosis of adamantinomatous craniopharyngiomas (aCPs) and of BRAF for that of papillary CPs (pCPs) in routinely processed surgical samples of non-adenomatous sellar lesions.

Methods: Forty-five cases of patients operated for non-adenomatous masses of the sellar region between 2004 and 2014 were retrieved from the files of the Anatomic Pathology unit of the Bellaria Hospital in Bologna, Italy. BRAF and CTNNB1 mutation status was analyzed by NGS in samples smaller than 1 cm(3) and histological re-evaluation was performed on all cases.

Results: CTNNB1 mutation analysis showed a sensitivity of 86.7 % and a specificity of 96.2 % for the diagnosis of aCPs. The specificity increased to 100 % considering that in one case, initially classified as a non-CP lesion (xanthogranuloma), the identification of a CTNNB1 S47R lead to histological re-evaluation and reclassification of the lesion as aCP. BRAF mutation analysis had a sensitivity of 76.9 % and a specificity of 96.4 % for the diagnosis of pCPs. The specificity increased to 100 % considering that in one case, initially classified as a Rathke cyst, the identification of BRAF V600E lead to histological re-evaluation and reclassification of the lesion as pCP.

Conclusions: This study confirms the diagnostic relevance of the molecular alterations recently identified in aCPs and pCPs and shows how the identification of BRAF and CTNNB1 mutations can be instrumental for the proper classification of samples that contain limiting amounts of diagnostic lesional tissue.