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

duct lobular unit complex (lobule) is the site of origin not only of LCIS but also the
bulk of DCIS (53).
Cancerization of lobules by duct carcinoma may have features that overlap with the
large-cell, apocrine type, and/or pleomorphic variants of LCIS. Admittedly, it would
be very difficult to distinguish cancerization of lobules by DCIS from these variants of
LCIS, especially if there were no "classical" areas of LCIS present in the biopsy.
Furthermore, how could one rule out the concomitant presence of LCIS and DCIS?
Cancerization of lobules by high-grade DCIS is usually quite easy to recognize. The
lesion contains large pleomorphic cells, areas of necrosis, and mitotic figures; lumens
are also often present. Yet, distinguishing LCIS from cancerization of lobules by a
low-grade, non-comedo, or small-cell DCIS could be problematic. Such distinctions
are not easy, likely arbitrary, and of uncertain clinicopathologic significance since the
two disease processes may be more alike than different. When in doubt, it is best to
favor low-grade DCIS and mention the LCIS patterns, so as to optimize both surgery
and patient follow-up.
Benign lesions that may be confused with LCIS (especially the signet-ring form) are
lactational changes and so-called clear-cell metaplasia of lobules. Clear-cell
metaplasia can also be confused with clear-cell variants of duct carcinoma (54,55).
The cause of focal lactational changes and clear cell metaplasia remains unclear, but
the cytologic features are benign, and once understood should not cause diagnostic
confusion (55).
When considering the diagnosis of recurrent in situ breast carcinoma in patients with
prior radiation therapy, radiation-induced atypia should be considered (56). The most
characteristic radiation effects produce atypical epithelial cells in the lobules
associated with lobular sclerosis and atrophy. Epithelial atypia in larger ducts, stromal
changes, and vascular changes were less frequent but are always accompanied by
prominent lobular changes. Mitotic figures in radiation-induced atypia are rarely, if
ever, seen. A final area of potential confusion is over diagnosing reactive foamy
histiocytes when present either adjacent to areas of duct ectasia or when insinuating
themselves between epithelial cells. These patterns mimic infiltrating histiocytoid
and/or lipid-cell carcinoma or pagetoid spread of lobular neoplasia into segmental
ducts.
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