RARE-63. CYST WALL OF ADAMANTINOMATOUS CRANIOPHARYNGIOMA CONTAINS TUMOR CELLS THAT COULD LEAD TO RECURRENCE AFTER SURGERY

BACKGROUND: Adamantinomatous craniopharyngioma (ACP) is the primary subtype of craniopharyngioma in children, frequently with mutations in exon 3 of the CTNNB1 gene. Most ACP consists of both a solid tumor and one or more cysts. Despite surgical resection of the solid tumor followed by radiation, recurrence involving the cystic component is common, suggesting that the cyst wall contains tumor cells. We present here conclusive molecular pathology evidence of the presence of tumor cells in the cyst wall similar to those in the solid tumor. METHODS: We used standard H&E staining and immunohistochemistry (IHC) to compare the histopathology characteristics between the matched cyst wall and solid tumor of 11 cases of ACP as well as their CTNNB1 expression and exon 3 mutation. RESULTS: Samples of the cyst wall and solid tumor were collected separately during the operation of 11 cases of ACP through careful dissection. The cyst wall showed the nested cell clusters and peripheral palisading epithelium which are identical to those in the solid tumor. The cyst wall and solid tumor both showed Ki67 and nuclear β-catenin expression by IHC. There is no difference in the transcription level of CTNNB1 between the cyst wall and the solid tumor, both being significantly higher than that in normal brain tissue. Exon 3 mutations of the CTNNB1 gene of the cyst wall and the solid tumor are identical in each case. CONCLUSION: Follow-up of clinical cases suggests that tumor cells in residual cyst wall may be the cause of recurrence after surgery.