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

display the reverse polarity typical of the papillary phenotype. This is revealed by the
detection of acid mucinous rims, lineal deposits of epithelial membrane antigen, and
microvilli in a peripheral position, even in areas where the micropapillae resemble
tubules. Most invasive micropapillary carcinomas are admixed with InvDC,NOS
and/or invasive mucinous carcinoma. Lymphatic vascular invasion is seen in 2/3rds of
cases, and the majority present with positive lymph nodes (8).
Differential diagnosis: Sclerosing papillary proliferations can be mistaken for
invasive papillary carcinoma. Fibrocystic changes containing florid intraductal
hyperplasia may undergo sclerosis, distortion, and entrapment of distorted ducts. This
benign lesion has been variously referred to as sclerosing papillary proliferation (31),
scleroelastotic lesion simulating malignancy (32), nonencapsulated sclerosing lesion
(33), indurative mastopathy (29), complex sclerosing lesion (34), invasive epitheliosis
(35), and radial scar (36,37). Duct adenomas also likely lie within the spectrum of
sclerosing papillary lesions (38-40).They are common lesions that can be mistaken for
invasive carcinoma, not only by mammogram, but also by gross appearance and light
microscopy. Indeed, Fenoglio et al. (31) state in their classic report that
"unfortunately, radical or modified mastectomies are still occasionally performed
because a distorted sclerosed benign papillary proliferation was misinterpreted as a
carcinoma, especially on frozen section."
In one series of 32 patients with sclerosing papillary proliferations (36), patients' ages
at diagnosis ranged from 30 to 57 years (mean, 43 years). After being observed from
15 to 24.5 years (mean, 19.5 years), only one of the 32 patients developed breast
carcinoma, a rate comparable to a control population. Furthermore, an autopsy study
failed to show a higher malignant potential for sclerosing papillary proliferations
(other than that expected in patients having fibrocystic changes). The investigators
suggested that only those sclerosing papillary proliferations containing high-risk
epithelial changes such as atypical hyperplasia and carcinoma in situ are associated
with increased risk of subsequent breast cancer development (37). Fibrocystic changes
and/or duct ectasia were also present in 88% of patients with sclerosing papillary
proliferations; in only 9% did sclerosing papillary proliferations occur as a single
lesion without fibrocystic changes (36). Multicentricity of sclerosing papillary
proliferations has been noted in 44% of cases (36). On mammogram, these lesions can
have an irregular stellate appearance and by gross exam, the lesions are gray-white to
yellow, stellate, firm densities, and sometimes have spiculated margins, features easily
confused with scirrhous carcinoma. Sclerosing papillary proliferations display a
central, relatively hypocellular core composed of dense, hyalinized connective tissue
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