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

In macroscopic appearance, phyllodes tumors are more or less circumscribed and are
composed of connective tissue and ductal epithelium, as are fibroadenomas; however,
in phyllodes tumors, the connective tissue shows greater cellularity. They are fleshy
tumors with spaces filled with leaflike (phyllodes) projections leaving residual
cleftlike spaces. The connective tissue component can contain foci of myxoid,
adipose, osseous, chondroid, and even rhabdomyomatous cells (132, 133). The
increased cellularity is often noted immediately adjacent to the cleftlike spaces lined
by epithelium, but this area of stromal condensation may be somewhat separated from
the epithelium by a grenz zone (134).
Although prediction of biologic behavior by histologic criteria is difficult with
phyllodes tumors, the World Health Organization considers it useful to separate cases
into three categories (benign, borderline, and malignant), which are based on the
extent of mitotic figures, infiltrative margins, cellular atypia, and cellularity. Local
recurrences are much more frequent than distant metastases. In a review of 187 cases,
Grimes reported an overall local recurrence rate of 28%, which was independent of the
degree of malignancy (benign 27%, borderline 32%, malignant 26%). No morphologic
features predicted recurrence. In this series, distant metastases occurred in 8 of 100
cases with follow-up (2 borderline and 6 malignant). Stromal overgrowth, mitotic rate
greater than 15 mitotic figures per 50 high-power fields, and cytologically atypical
cells characterized seven of the eight metastasizing tumors. The high local recurrence
rate of phyllodes tumors suggests multifocal growth as reported by Salm. Similar,
multifocal fibroadenomas can occur in women and men; when florid, they are referred
to as fibroadenomatoid hyperplasia (135).
In a review of 26 cases, Ward and Evans studied a number of clinicopathologic
features (tumor size, stromal overgrowth, tumor necrosis, mitotic rate, stromal
cellularity, nuclear size, nuclear pleomorphism, specialized stroma, and initial
therapy) and correlated their ability to predict local recurrence, uncontrolled local
recurrence, and distant metastases. Of the 26 tumors, 7 caused death (5 from
metastases and 2 from extensive local recurrence), and 6 of the 7 had stromal
overgrowth, defined as mesenchymal proliferation with complete absence of a ductal
epithelial element in an area greater than one low-power (x40) field (excluding
occasional broad stromal portions of epithelium-lined papillary structures that could,
by carefully selecting a given field, fulfill this criterion). With the exception of tumor
necrosis (not infarct), which appeared dependent on stromal overgrowth, all the other
studied factors were not significantly related to clinical behavior. Likewise, Hart and
colleagues stressed the importance of stromal overgrowth in predicting metastasis.
Some tumors may have to be extensively sampled to find the focal area of stromal
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