Phyllodes Tumor (Cystosarcoma Phyllodes) Workup

Updated: Jun 20, 2016
  • Author: Donald R Lannin, MD; Chief Editor: John Geibel, MD, DSc, MSc, AGAF  more...
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Laboratory Studies

No specific hematologic tumor markers or other blood tests can be used to diagnose phyllodes tumors, though expression of biologic markers can discriminate between different grades of tumor. [12, 13] The immunohistochemical expression of CD10 can predict the occurrence of distant metastasis. [14] Investigation of a malignant phyllodes tumor with whole genomic and proteomic analysis revealed chromosome mutations, amplifications, and deletions. [15] Further exploration of the biology of phyllodes tumor may lead to the development of targeted treatments.


Imaging Studies

Although mammography and ultrasonography generally are important in the diagnosis of breast lesions, they are notoriously unreliable in differentiating benign phyllodes tumors from malignant phyllodes tumors or from fibroadenomas. (The phyllodes tumor’s mammographic appearance, as a round density with smooth borders, is similar to that of fibroadenoma.) Thus, findings on imaging studies are not definitively diagnostic of phyllodes tumors. [16]



Open excisional breast biopsy for smaller lesions and incisional biopsy for large lesions are the definitive methods for diagnosing phyllodes tumors. Fine-needle aspiration (FNA) for cytologic examination usually is inadequate for the diagnosis of phyllodes tumors. Core biopsy is more reliable, [17]  but sampling errors may still occur, and it may still be difficult to distinguish the lesion from a fibroadenoma.


Histologic Findings

All phyllodes tumors contain a stromal component that can vary significantly in histologic appearance from one lesion to another. [14]  In general, benign phyllodes tumors demonstrate a markedly increased number of regular fusiform fibroblasts in the stroma. Occasionally, highly anaplastic cells with myxoid changes are observed. A high degree of cellular atypia, with increased stromal cellularity and an increased mitotic count, is almost always observed in malignant phyllodes tumors.

Ultrastructurally, in both benign and malignant forms of phyllodes tumors, nucleoli may reveal a coarsely meshed nucleolonema and abundant cisternae in the endoplasmic reticulum.



The World Health Organization (WHO) divides phyllodes tumors into the following three categories [18] :

  • Benign (grade 1)
  • Borderline (grade 2)
  • Malignant (grade 3)