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

component amid that stromal overgrowth. Although most recurrent phyllodes tumors
have both epithelial and stromal elements, some may recur entirely as stromal
sarcomas. Nonetheless, so-called stromal sarcoma of the breast should be
differentiated from malignant phyllodes tumor. Indeed, the term stromal sarcoma of
the breast ought to be discarded and primary sarcomas designated by their pattern of
differentiation (fibrosarcoma, undifferentiated sarcoma/malignant fibrous
histiocytoma, osteosarcoma, liposarcoma, etc.). Jones and colleagues have reviewed
32 cases of fibrosarcoma and malignant fibrous histiocytoma of the breast. They were
able to separate them into low- and high-grade tumors. Whereas none of the low-grade
tumors metastasized, 25% of the high-grade tumors spread to distant sites (a rate
higher than for malignant phyllodes tumors). Breast sarcomas with giant cells and
osteoid (osteogenic sarcoma) are also reported to cause death in most patients with
these high-grade sarcomas (140).
Some authors have used the term “cellular periductal stromal tumor” as an alternative
for cystosarcoma phyllodes; but Dr. Tavassoli (65) uses the term periductal stromal
sarcoma for an even rarer biphasic breast tumor, characterized by a cellular
sarcomatous spindle-cell proliferation oriented around breast ducts that retain lumens
without the leaf-like (“phyllodes”) processes. A relative new entity has now been
added to the mix. Leibl and Moinfar (141) have reported 7 mammary sarcomas that
did not fit into any specific soft tissue sarcoma category. Histologically, they were
composed of spindle cells with highly pleomorphic nuclei and abundant mitoses.
Whereas CKs, CD34, desmin, and h-caldesmon were not expressed, all tumors were
positive for CD10 and vimentin. CD29 and SMA were observed in 3 cases each
(43%), and p63 and calponin in 2 cases each (29%). Other myoepithelial markers and
steroid receptors were absent, except androgen receptors, which were expressed in one
sarcoma. Five sarcomas showed positivity for EGFR. The distinction of specific,
histogenetically defined sarcoma entities (such as leiomyosarcoma, angiosarcoma,
liposarcoma) from NOS-type sarcoma with CD10 expression is usually clear-cut
because the former exhibit a characteristic histomorphology and immunoprofile.
Phyllodes tumors with stromal overgrowth or recurrent phyllodes tumors lacking
epithelial structures as well as periductal stromal sarcomas can be ruled out by their
frequent expression of CD34 and negativity for myoepithelial markers. The most
important differential diagnosis is sarcomatoid metaplastic carcinoma, because its
treatment includes axillary lymphadenectomy. But, distinction from sarcomatoid
carcinoma can be extremely difficult and requires extensive immunohistochemical
evaluation for CKs and myoepithelial markers. The immunophenotype of NOS-type
sarcomas with CD10 expression suggests that these neoplasms represent a mammary
sarcoma variant with myoepithelial features.
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