[Implication of BRAF V600E and CTNNB1 gene mutations in the pathological classification of craniopharyngioma]

Objective: To investigate the clinicopathological significance of BRAF V600E and CTNNB1 gene mutations in adamantinomatous craniopharyngiomas (ACP) and papillary craniopharyngiomas (PCP). Methods: The retrospective study included a total of 67 craniopharyngiomas diagnosed from October 2009 to August 2018 at Xuanwu Hospital, Capital Medical University. The immunohistochemical staining for β-catenin and BRAF V600E expression, Sanger sequencing of exon 3 of CTNNB1, BRAF mutation analysis by scorpions amplification refractory mutation system (ARMS) fluorescence quantitative PCR were performed. Univariate survival analysis was used to correlate with tumor recurrence. Results: Of the 67 patients, 53 were ACPs and 14 were PCPs. Four patients underwent multiple operations and one of them presented with malignant transformation into squamous cell carcinoma. Histologically, ACPs were characterized by whorl-like cell clusters, peripheral palisaded layer, stellate reticulum, finger-shaped protrusions, ghost cells and wet keratinous substances. While PCPs usually consisted of mature squamous epithelium associated with fibrovascular stroma resulting in papillary appearance. The nuclear immunopositivity for β-catenin was observed in 73.6% (39/53) of ACPs, and it was absent in PCPs (0/14). The nuclear translocation of β-catenin usually presented at whorl-like structures or around ghost cells. Of all the cases, mutations analysis in exon 3 of β-catenin gene CTNNB1 were successful in 46 cases and 42.1% (16/38) of ACP showed CTNNB1 gene mutation, while none of the PCPs harbored CTNNB1 gene mutation (0/8). The cytoplasmic immunopositivity for BRAF V600E mutant protein was found in all PCPs (14/14) and negative in all ACPs (0/53). ARMS-PCR results showed that BRAF V600E mutations were observed in 13/14 of PCPs but not seen in ACPs (0/53). Follow-up data were available in 35 patients with duration of 2 to 120 months. Ten patients experienced recurrences after the first surgery. Upon univariate survival analysis, only subtotal excision was found to be associated with increased recurrence (P=0.032), while pathological type, postoperative radiotherapy and CTNNB1 gene mutation were not (P>0.05). Conclusions: There is significant difference in the expression of BRAF V600E and CTNNB1 genes between ACP and PCP, and their immunohistochemical and molecular detection therefore can be used in the diagnosis and differential diagnoses of craniopharyngiomas.