Description
Metaplastic carcinomas of the breast (MCBs) are unusual neoplasms
characterized by an admixture of glandular epithelial
components, which frequently exhibit features of squamous
differentiation, and mesenchymal malignant components. Regardless
of the presence of myoepithelial features in MCB, no
consensus concerning their putative histogenesis has yet been
achieved. Recently, novel putative myoepithelial markers have
been developed, including p63, maspin, and P-cadherin. We
assessed the expression of these myoepithelial markers in
MCBs and compared their expression with classic myoepithelial
markers. Immunohistochemistry using the streptavidin–
biotin–peroxidase complex technique with antibodies raised
against p63, maspin, P-cadherin, actin (clones CGA7, 1A4 and
HHF35), cytokeratin 14 (Ck14), and vimentin was performed
on 16 MCBs (7 matrix-producing MCBs, 6 adenosquamous
MCBs, and 3 MCBs with heterologous elements). In healthy
breast lobules and ducts adjacent to the tumors, myoepithelial
cells showed distinctive and consistent immunoreactivity for
p63, maspin, P-cadherin, actin, S-100 protein, and Ck14. Matrix-
producing MCBs were positive for maspin in all cases, for
p63 in 4 of 7 cases, and for P-cadherin in 4 of 7 cases. Adenosquamous
MCB showed immunoreactivity for p63, maspin,
and P-cadherin in 5 of 6 cases. All novel myoepithelial markers
and Ck14 decorated squamous cell islands. MCBs with heterologous
elements were positive for p63 in 1 case, for maspin in
all 3 cases, and for P-cadherin in 2 cases. All cases showed at
least one of the novel myoepithelial markers. Eleven of 16
cases were positive for actin. Eleven of 14 cases reacted with
Ck14, and all cases that stained for S-100 protein (9 of 9) and
vimentin (13 of 13) were also positive. Based on our findings,
the balance of probabilities favors that MCBs may have a basal
or myoepithelial cell histogenesis and differentiation.
; Milanezi, Fernanda 
