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

implies a relative risk for development of invasive cancer of 1.5- to 2.0-fold above
that of the general population (80).
Although most examples of sclerosing adenosis are easily diagnosed, this lesion is
misinterpreted as invasive carcinoma more than any other benign breast lesion (80,
81). Sclerosing adenosis occurs most commonly in the childbearing ages and
perimenopausal years (80-83).
Sclerosing adenosis is composed of a cellular proliferation of both duct luminal cells
that form acini and spindled myoepithelial cells that impart a sclerotic quality. An
important diagnostic feature is that sclerosing adenosis grows within and expands
lobules (often in multiple adjacent foci to form an aggregate) while maintaining the
circumscribed, lobulocentric pattern of benign breast lobules. This lobulocentric
growth has a whorled and pseudoinvasive quality. Like invasive carcinoma, sclerosing
adenosis may show perineural "invasion" and involve vessel walls (84).
Foci of sclerosing adenosis can occasionally merge with areas consistent with
microglandular adenosis, a related lesion that shows a more haphazard proliferation of
benign glands (85). Both sclerosing adenosis and microglandular adenosis maintain a
well-developed basal lamina around glands, a feature that can be highlighted by
immunohistochemical stains for type IV collagen or laminin (86). Moreover, in
sclerosing adenosis, duct luminal cells are surrounded by myoepithelial cells, which
bind with antibodies to smooth muscle actin (86).
When sclerosing adenosis is involved by carcinoma in situ (most commonly LCIS, but
it may be DCIS), the pattern mimics invasive carcinoma (87). Antibodies reactive for
smooth muscle actin, calponin, and/or p63 can be used to demonstrate the intact
myoepithelial cells to assist in distinguishing carcinoma in situ within sclerosing
adenosis from invasive carcinoma (88).
Myoepithelial cells are known to be components of both benign and malignant tumors
of sweat, salivary, and mammary gland origin (38-41, 89-108). In these tumors,
myoepithelial cells can demonstrate squamous, chondromyxoid, plasmacytoid, clear
cell, and myoid spindle-cell differentiation (38-41, 89-108). Pure myoepithelial cell
tumors are called myoepitheliomas, and those also containing glandular elements are
called adenomyoepitheliomas (89).
Adenomyoepitheliomas of the breast have been well documented in the Englishlanguage
literature (109). Some of these tumors are described as either
myoepithelioma or leiomyosarcoma (89, 110). Yet the bulk of the English-language
literature indicates that adenomyoepitheliomas present as breast masses (on average, 2
to 3 cm) in the same age range as for patients with breast carcinoma. They are firm to
90