Collagenous spherulosis mimicking keratinizing squamous metaplasia in a borderline endometrioid tumour of the ovary

Abstract

Aims: Collagenous spherulosis (CS) is a rare lesion which is an incidental finding in breast and salivary glands. It is characterized by fibrillar spherules exhibiting an intrinsic radiating or concentric pattern which are surrounded by myoepithelial cells. This entity can be misdiagnosed as adenoid cystic carcinoma and in-situ ductal carcinoma. Methods and results: We report here the first case of CS arising in a borderline endometrioid tumour of the ovary where it merged with squamous metaplasia. Conclusion: This observation illustrates another pitfall of CS which can be misidentified as keratin pearls. The pathogenesis remains unclear but it has been claimed that the accumulation of basement membrane material may be due to the proliferation of pre-existing myoepithelial cells that secrete matrix components. Since ovarian tumours do not contain myoepithelial cells, one should assume that the epithelial cells differentiate towards myoepithelial cells as it has been shown in vitro and ex vivo.