A 52 years old female presented with a large (~ 10 cm) right breast mass, almost completely replacing the breast tissue. A core needle biopsy was performed.

Contributed By: Kamaljeet Singh MD

Please choose:

  • Dermatofibrosarcoma protuberans

  • Angiosarcoma

  • Fibromatosis

  • Spindle cell type metaplastic carcinoma

  • Malignant phyllodes tumor






The answer is Malignant Phyllodes Tumor.



Malignant phyllodes tumor

The biopsy shows a cellular spindle cell proliferation with staghorn-shaped thin-walled vessels. The spindle cells show nuclear atypia (hyperchromasia and pleomorphism) suggesting neoplastic proliferation and indicating malignant nature. High magnification (last picture) shows portion of a benign epithelial structure (duct). No vasoformative areas are noted. The differential diagnosis of spindle cell proliferation in breast is limited, but it can be difficult. Angiosarcinoma is the most common breast sarcoma and other types of primary sarcomas of breast are vanishingly rare. Most sarcoma-like elements in breast tumors are considered to be the mesenchymal/heterologous differentiation in a metaplastic carcinoma or a malignant phyllodes tumor.

So, the two main differential diagnoses are metaplastic carcinoma and malignant phyllodes. The immunohistochemical stains for keratin (MNF116, HMWK, AE1/AE3, keratin5/6) and p63 were negative on biopsy. The diagnoses of malignant spindle cell lesion with a differential diagnosis of metaplastic carcinoma and phyllodes were raised.  On mastectomy tumor focally showed a phyllodes type architecture and repeat keratin stains and p63 were negative. A diagnosis of malignant phyllodes was rendered.

Malignant phyllodes is the least common type of fibroepithelial lesion and they develop 2-5 years later than their benign counterparts. With classic histological changes of leaf-like architecture, malignant phyllodes can be diagnosed on a biopsy. However in the absence of an epithelial component it may be difficult to pin-down the fibroepithelial nature of the lesion. On excisional tissue the diagnosis of malignant phyllodes is often straightforward. Histological features of malignant phyllodes may include stromal overgrowth, diffuse increase in stromal cellularity, marked stromal nuclear atypia, high mitoses, stromal overgrowth, and malignant heterologous elements.

Reference: Reference: WHO classification of Tumours Editorial Board. Breast tumours. Lyon (France): IARC; 2019 (pages 172-175).