33 Special Types of Invasive Breast Carcinoma: Diagnostic Criteria ...

overgrowth (136).
While acknowledging that there were no consistently reliable morphologic landmarks
for predicting outcome, Azzopardi stated that features favoring benign behavior are 1)
pushing or well-demarcated tumor border at the microscopic level 2) even distribution
of epithelial tissues within the tumor, and 3) less than 3 mitotic figures per 10 highpower
fields, and 4) bland cytologic features with low cellularity. In contrast, features
favoring malignant behavior are 1) infiltrating tumor margin, 2) connective tissue
growth outstripping epithelium-lined structures, and 3) more than 3 mitotic figures per
10 high-power fields, and 4) pronounced cellular atypia with high cellularity.
When phyllodes tumors occur in women younger than 20 years, they are almost
always benign, despite clinical and histologic features of malignancy (137, 138). Flow
ploidy or S phase fraction determinations do not appear to reliably predict behavior
(74).
Proper initial therapy (wide local excision) is helpful in controlling local recurrence
but appears irrelevant in preventing distant metastases (129). Simple mastectomy
should be reserved for large tumors, which for all practical purposes preclude breast
conservation, and also for cases with multiple recurrences because some recurrent
tumors may progress to higher grade tumors or cause death by invasion of the chest
wall. Axillary metastases are rare.
Distinguishing cellular fibroadenoma from benign phyllodes tumor may be more of an
academic exercise than a practical one because both are easily managed by
conservative local therapy, even with recurrence (73, 74). However, borderline and
malignant phyllodes tumors can develop uncontrolled local recurrence or distant
metastases and should be distinguished from cellular fibroadenoma. Careful
application of the criteria outlined before should avoid a misdiagnosis. Also worth
noting is that, like the mammary stroma (139), fibroadenomas may contain
multinucleated stromal giant cells, which can be mistaken for malignant cells (62).
Some fibroadenomas have also been mistaken for phyllodes tumors because they
show prominent smooth muscle differentiation (61), fatty tissue metaplasia (62), or
carcinomatous transformation (77). Hiraoka and associates have described a phyllodes
tumor of the breast containing intracytoplasmic inclusion bodies identical with
infantile digital fibromatosis.
Whereas extensive tumor sampling may be necessary to reveal stromal overgrowth in
a phyllodes tumor, extensive sampling may also be necessary to find the epithelial
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