Malignant phyllodes tumour of the breast mimicking endometriosis

• DOI: 10.1007/s00428-021-03086-6
• Publication Date: 2021-03-29T22:02:16Z
• Authors: Andrew H. S. Lee; Ulises Zanetto; Rachna Awasthi; Mei-Ju Hwang; Nur Diyana Md Nasir; Cedric Chuan Youn...; Bin Tean Teh; Puay Hoon Tan
• Keywords: 03 medical and health sciences; 0302 clinical medicine

A 63-year-old woman presented with a clinically malignant mass. Core biopsy showed features resembling endometriosis. The glands were GATA3 and oestrogen receptor positive consistent with mammary origin and had no myoepithelial layer. The excision also showed a fibroepithelial component with stromal overgrowth, frequent mitoses and invasive margin consistent with a malignant phyllodes tumour. KMT2D and SETD2 mutations were present in both the conventional phyllodes tumour and endometriosis-like areas and are also described in endometriosis raising interesting questions about these lesions. This unusual pattern is a potential diagnostic pitfall, so it is helpful to be aware of it.