Case 5 -
Malignant Phyllodes Tumor
Prince of Wales Hospital
Hong Kong, China
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A 50 year old lady presented with a 4.7 cm mass in the right breast. There was no nipple discharge.
There was also a previous history of breast lump removed from the same breast 2 years ago. Physical
examination showed the mass to be hard to palpation, but was not adherent to the skin or underlying
tissue. There was no axillary lymphadenopathy.
The breast lump was excised and the section is a representative sampling of this breast mass.
Fibroepithelial Lesions- Fibroadenoma
Within the group of fibroepithelial lesions, fibroadenomas and phyllodes tumors share the histologic
feature of intimate association of the epithelial and stromal components, the latter being derived
exclusively from the interlobular specialized stroma. The usual fibroadenomas are readily recognized and
do not pose any diagnostic challenges. Juvenile fibroadenoma may present with a more worrisome clinical
history of rapid growth, and histologically it may be endowed with high stromal cellularity, with a
predominantly pericanalicular pattern and mitotic figures may be seen among the stromal cells. The
relatively uniform stromal proliferation and absence of true sarcomatous stroma or stromal overgrowth
help to differentiate juvenile fibroadenoma from phyllodes tumor. The behavior and prognosis of juvenile
fibroadenoma is similar to other fibroadenomas .
Fibroepithelial Lesions - Phyllodes Tumor
Phyllodes tumor is an uncommon breast tumor, and is estimated to account for less than 1% of primary
breast tumors . There appears to be ethnical difference, with a higher incidence occurring in Asians.
In general the patient's age for phyllodes tumor is about 15-20 years older than that for fibroadenoma.
Patient with phyllodes tumor presents with a history of rapidly enlarging breast lump. Microscopically,
phyllodes tumor is characterized by variable degree of stromal proliferation, resulting in distortion of
the architecture to give a leaf like pattern. In general, there is increased stromal cellularity,
particularly in areas that are in close contact with the epithelium. The stromal cells may also show
nuclear crowding, atypia and increased mitotic activity. Stromal overgrowth may be present; and the
margin of the phyllodes tumor may vary from well delineated to infiltrative. The epithelial cells may
occasionally show squamous or apocrine metaplasia or epithelial hyperplasia.
Phyllodes tumor are usually graded into benign, borderline and malignant . A malignant phyllodes
tumor is characterized by stromal hypercellularity, significant stromal cell atypia or nuclear
pleomorphism, the presence of malignant heterologous elements (osteoid or chondroid), increased mitotic
activity (3-4 or more mitoses per 10 high power fields) and the presence of infiltrative margin and
Sometimes, the stromal overgrowth may be so prominent that the benign
epithelial element may only be found after diligent search. In a typically benign phyllodes tumor, the
stroma is also cellular, especially when compared to fibroadenoma, and the stromal cell nuclei are
monomorphic and mitoses are rare, and the margin is better delineated. Borderline phyllodes tumor tend
to show intermediate features. Thus the histomorphology of different grades of phyllodes tumors lie in a
The outcome of phyllodes tumor is recurrence and systemic metastasis. Local recurrence occurs in all
grades of phyllodes tumors, and the histology may be similar or may progress to a higher grade lesion.
Metastasis tends to be systemic rather than lymph node as phyllodes tumor behaves more like a sarcoma
than carcinoma, and the metastasis may only contain the stromal component devoid of epithelium . The
frequency of recurrences and metastases differ in different series, but the rate for both events
increases from benign to borderline to malignant phyllodes.
The differentiation between the various phyllodes tumor and fibroadenoma is particularly problematic
in core needle biopsies. The difficulty stems from the intrinsic limited sampling in core biopsy and the
heterogeneous stromal cellularity in phyllodes. About 70% of phyllodes tumors at excision were diagnosed
as fibroadenoma on core biopsy
Features that were found to be useful for diagnosing phyllodes
(over fibroadenoma) in core
biopsies include increased stromal cellularity
fragmentation, adipose tissue within stroma , higher mitotic rate and proliferative index as measured
by Ki67 staining .
Metaplastic Carcinoma (Spindle Cell Carcinoma) and Sarcoma
Metaplastic carcinoma is characterized morphologically by highly pleomorphic malignant cells, with
some (monophasic) showing only spindle cell (sarcomatoid)
pattern . Primary breast sarcoma also shows
proliferation of malignant spindle cells, which can range from spindled to pleomorphic. These entities
can be differentiated from malignant phyllodes tumor by the presence of benign epithelial element in
phyllodes tumor but not in others. Immunohistochemistry may be helpful, as epithelial markers for
cytokeratins like AE1/3 or CAM5.2, and p63  are positive for metaplastic carcinoma, whereas CD34 has
been reported to be positive for phyllodes tumor .
Malignant phyllodes tumor.
Breast, phyllodes tumors, sarcoma, metaplastic carcinoma
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