Microcystic stromal tumour of the ovary: frequent mutations of β-catenin (CTNNB1) in six cases

Aims To analyse the clinicopathological, immunohistochemical and β‐catenin (CTNNB1) mutation characteristics of six cases of microcystic stromal tumour of the ovary (MCST). Methods and results Six Chinese patients with MCST who ranged in age from 29 to 69 years (mean 50 years) were included in the study. Five patients were detected with a pelvic mass during routine health examinations and one patient presented initially with opsomenorrhoea. All tumours involved the left ovary, with solid‐cystic cut surface in five cases and cystic cut surface in one case. Microscopically, microcysts, solid nests and hyaline degenerated fibrous stroma were variably mixed. Immunohistochemically, the tumour cells in all cases were diffusely positive for CD10, vimentin and WT‐1 and negative for α‐inhibin and calretinin. β‐catenin expression was observed in both the nucleus and the cytoplasm in five cases and only in the cytoplasm in one case. The results of CTNNB1 mutation analysis revealed four missense point mutations in four cases, which were c.97T>C, c.101G>A, c.110C>G and c.122C>T. Conclusions MCST shows a unique morphology with characteristic immunophenotype. β‐catenin expression in the nucleus and β‐catenin mutations were identified in the majority of cases, which suggests that the Wnt/β‐catenin pathway may play a crucial role in the tumorigenesis of MCST.