Phyllodes tumors range from benign to malignant and often clinically mimic a fibroadenoma. They are, however, distinct neoplastic lesions derived from monoclonal stromal cells and because of their malignant potential are managed by surgical excision.

Symptoms
Patients will present with a single discrete, nontender lump and may provide a history of increase in size.

Signs
Phyllodes tumors are usually unilateral, single, well-circumscribed, mobile and firm in consistency.

Radiology
Imaging features are generally very similar to those of a fibroadenoma.

Mammography
Phyllodes tumors appear as well-defined oval or round soft-tissue densities.

They have a lobulated or smooth-outline. Unlike fibroadenomas, calcification is rarely seen. The masses are frequently large and may grow quickly on sequential examinations.

Ultrasound
Phyllodes tumors tend to be well-circumscribed, lobulated or smooth-outlined, hypoechoic mass lesions with a homogeneous internal echo pattern. Cyst-like spaces may be seen within the stroma. Heterogeneity of the internal echo pattern may indicate associated hemorrhage or necrosis.

Frequently, phyllodes tumors are highly vascular on color-flow doppler, although this is unreliable in distinguishing benign from malignant change.

Pathology
Macroscopic Appearance
Phyllodes are usually well-circumscribed, firm, lobulated masses. The cut surface is yellowish-white and often has a mucoid consistency with obvious clefts surrounding “leaf-like processes” from which the lesion takes its name.

They may be indistinguishable from fibroadenoma.

Microscopic Appearance
Like fibroadenomas, phyllodes tumors are composed of a stromal and an epithelial element. The epithelia component comprises ductal structures with invaginations into the lumina caused by the proliferating stroma.

These are the “leaf-like” structures. The epithelial component, like that in fibroadenoma, may show varying degrees of usual-type hyperplasia. The significant component in these lesions however is the stroma which is invariably cellular. The appearance of the stroma ranges from regular cellularity similar to that seen in a cellular fibroadenoma to marked hypercellularity including mitoses which may be frequent and may include abnormal forms.

The appearance of the stromal cells varies from plump, regular spindle cells to pleomorphic cells with features of sarcomatous change.

These lesions are divided into low-grade, intermediate-grade and high-grade categories based on the presence and degree of stromal overgrowth, the cytologic characteristics of the stromal cells, the number of mitoses per 10 high-power microscope fields and the nature of tumor margin (pushing or infiltrative). No single feature has proved reliable in predicting clinical outcome; however, this constellation of characteristics has been shown by several small studies to be of some use.

Management
All phyllodes tumors must be excised with an adequate margin of excision.  These lesions must not be enucleated but excised completely, with a surrounding rim of normal breast tissue. Large tumors may need mastectomy with immediate reconstruction to achieve adequate clearance. Failure to do so will result in an unacceptable local recurrence rate and the potential for malignant transformation.

A.D. Purushotham, P. Britton and L. Bobrow
A prospective study of benign breast disease and the risk of breast cancer. JAMA 2002

References