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

Sclerosing papillary proliferations (aka, radial scars) are most frequently confused
with invasive, well-differentiated (tubular) carcinomas. Invasive tubular carcinomas
can (23), but usually do not display the zonal character of sclerosing papillary
proliferation (central hypocellular core surrounded by proliferative fibrocystic changes
in a radial fashion). In addition, the pseudoinvasive glands of sclerosing papillary
proliferations may display a double row of cells (myoepithelial cell layer adjacent to
luminal epithelial cells) encased in a hyalinized, elastic tissue-rich stroma. Glands of
invasive tubular carcinoma are composed of a single row of atypical cells encircled by
relatively loose, desmoplastic stroma. Furthermore, the pseudoinvasion of sclerosing
papillary proliferations is limited to the immediate periductal zone; involvement of the
interlobular fat would suggest a true carcinoma. Both microglandular adenosis and
sclerosing adenosis can involve fat (34-36,23). Finally, sclerosing papillary
proliferations (like other forms of fibrocystic changes) can occur concomitantly with
atypical hyperplasia, carcinoma in situ, and invasive carcinoma. A recent study (37)
reported that atypical hyperplasia and/or carcinoma rarely associated with sclerosing
papillary lesions less than 6 cm in size in women under 40 years of age. Usual
histologic criteria for atypia and carcinoma should be applied in making the diagnoses.
Duct adenoma of the breast, which is likely a variant or within the spectrum of
sclerosing papillary lesions, is a benign lesion that should be considered in the
differential diagnosis of invasive tubular carcinoma (38,39). Lammie and Millis (39)
concluded that ductal adenomas evolved by sclerosis of benign intraductal papillary
lesions, although sclerosing adenosis and duct ectasia showed similarities. Azzopardi
(38) noted similarities between papilloma and salivary-type adenoma. Duct adenomas
are adenomatous nodules occurring in small to medium-sized ducts surrounded by
densely fibrous walls. These lesions have a circumscribed, variably lobated outline,
often with a central scar. Fibrous distortion leads to pseudoinvasion of central or
adjacent tissues. Worrisome atypia can also occur, especially when apocrine
metaplasia is present. But, demonstrating the well-circumscribed outline and the
biphasic epithelial-myoepithelial differentiation are reliable criteria for recognizing
this lesion as benign (38,39). Core needle biopsies of these tumors can be especially
treacherous, when the lobulocentric character of duct adenoma cannot be readily
appreciated.
Finally, tubular carcinoma needs to be differentiated from invasive lobular carcinoma,
tubulolobular variant (40). This should not be difficult, since the invasive components
of the latter neoplasm form not only small tubules, but also cords of cells more
characteristic of invasive lobular carcinoma. Tubulolobular carcinoma has been
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