Abstract
Invasive lobular carcinomas (ILC) of breast typically demonstrate intracytoplasmic mucin. We present a unique case of classical type ILC with abundant extracellular mucin and strong ERBB2 (HER2/neu) expression confirmed by immunohistochemistry and fluorescent in situ hybridization. Dual E-cadherin/p120 immunohistochemical stain demonstrated complete loss of membranous E-cadherin and the presence of diffuse cytoplasmic p120 staining, confirming the lobular phenotype. The tumor cells showed ductal-like cytoplasmic MUC1 staining, but were negative for MUC2 and other mucin gene markers. In addition, studies of tissue microarrays of 80 breast carcinomas with mucinous differentiation revealed 4 pure mucinous carcinomas showing significantly reduced E-cadherin staining without redistribution of p120 into cytoplasm. The findings suggest that the presence of extracellular mucin does not exclude a diagnosis of lobular carcinoma, and the morphologic and molecular characteristics of lobular and ductal carcinomas are more complex than previously appreciated.
Highlights
Ductal carcinoma and lobular carcinoma are traditionally considered two distinct types of mammary carcinoma with characteristic morphology, immunohistochemical profile, and clinical behavior
In order to investigate whether lobular phenotype is a rare variant of extracellular mucin-producing carcinoma of breast, we studied tissue microarrays of 80 breast carcinomas with mucinous differentiation, including 40 pure mucinous carcinomas and 40 carcinomas with mixed mucinous and non-mucinous components
Since the term lobular carcinoma was coined by Foote and Stewart in 1941 [14], it had long been accepted that
Summary
Ductal carcinoma and lobular carcinoma are traditionally considered two distinct types of mammary carcinoma with characteristic morphology, immunohistochemical profile, and clinical behavior. The classification of ductal versus lobular carcinoma is routinely based on the growth pattern and cytology of the tumor cells. Invasive lobular carcinomas (ILCs) are characterized by cytologically uniform cells with round nuclei and inconspicuous nucleoli, as well as discohesive architecture with linear or non-linear growth pattern. A variable portion of ILC cells show intracytoplasmic mucin secretion and demonstrate signet-ring cell morphology. Lobular carcinoma has been considered a variant of mucin-secreting carcinoma with only intracytoplasmic mucin [1,2,3,4]. A diagnosis of mucinous carcinoma or ductal carcinoma with mucinous features is often made in the presence of
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