Three cases of an unusual pattern of invasion in malignant Brenner tumors

Ovarian malignant Brenner tumors are rare neoplasms that are typically admixed with benign and borderline Brenner tumor elements. We report 3 cases of an unusual variant of malignant Brenner tumor where the infiltrative malignant component arose directly from a benign Brenner tumor rather than from borderline elements and did not exhibit a desmoplastic stromal response. Borderline elements were present in 1 case, but the invasive component did not arise from these. Our cases highlight that an absence of a borderline element should not dissuade the pathologist from diagnosing a malignant Brenner tumor.