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

Collagenous spherulosis is a recently-described benign breast lesion composed of a
proliferation of duct Luminal cells and myoepithelial cells, which make abundant
basement membrane material (44, 45). That collagenous spherulosis can be over
diagnosed as a malignant neoplasm was demonstrated by Clement et at. (44) who
reported that one of their initial 15 cases of collagenous spherulosis had been
inappropriately called adenoid cystic carcinoma and three others, intraductal
signet-ring carcinoma. Typically, to date, patients with collagenous spherulosis are
women of from 39 to 55 years of age (mean, 41 years), who have had a breast biopsy
or simple mastectomy because of the presence of a palpable mass, abnormal
mammogram, or both. Collagenous spherulosis is an incidental microscopic finding,
which can be unifocal or multifocal. The lesions occur in duct lumens and consist of
intraductal hyperplastic cells containing focal aggregates of well-circumscribed,
acellular spherules ranging in size from 20 to 100 µm. At low power, collagenous
spherulosis resembles a form of cribriform intraductal carcinoma. The spherules are
usually discrete but can coalesce and range from a few to up to 50 within any given
focus. The spherules stain pink-red and appear fibrillar with hematoxylin and eosin
(H&E); many have a pale center and more darkly staining periphery. The fibrillar
components are arranged in a concentric laminated pattern, or radiate in a star-shaped
configuration, or both. Outlining the spherules in all cases seen are cells (actually
myoepithelial cells) that appear to be stretched or flattened around them in some areas.
Epithelial cells identical to those found in typical duct hyperplasia can also be seen
(45). Adjacent breast tissue frequently contains fibrocystic changes with duct
hyperplasia, sclerosing adenosis, and/or intraductal papilloma.
Intraductal signet-ring carcinoma (1, 46) should be considered in the differential
diagnosis. Intraductal signet-ring carcinoma is a rare lesion composed of large,
malignant cells that are vacuolated (46). The vacuoles are periodic acid-Schiff (PAS)
positive (as are the spherules of collagenous spherulosis) but, in contrast to
collagenous spherulosis, they are negative with collagen stains. A clear understanding
of collagenous spherulosis may make it possible to distinguish it from intraductal
signet-ring carcinoma.
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