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

The classical pattern of infiltrating lobular carcinoma is that of diffuse and/or
multifocal (i.e., discontinuous) infiltration of small, round, regular tumor cells
arranged in single file between collagen bundles, which sometimes encircle ducts in a
targetoid or onionskin fashion. Occasional lesions form foci of small tubules, referred
to as the “tubulolobular variant of infiltrating lobular carcinoma.” DiCostanzo et al.
(9) detected LCIS associated with 65% of 176 classic infiltrating lobular carcinomas
and 57% of 54 variant tumors. In my experience, when studied with
immunoperoxidase techniques, classical invasive lobular carcinoma has always been
positive for hormone receptors. This may not be true for the more poorly
differentiated variant forms.
Pleomorphic infiltrating lobular carcinoma has a pattern of infiltration similar to that
of the classical variant (best appreciated at low magnification); however, the nuclei are
more pleomorphic and they display varying degrees of contour irregularity, more
prominent nucleoli, greater hyperchromaticity, increased chromatin clumping and
mitotic activity, and/or greater nuclear size (grade 2 or 3 nuclei) than do the nuclei of
the classical variant. The degree of nuclear atypia can approach that found in
infiltrating duct carcinomas, but, the invasive pattern characteristic of the classical
lobular variant is always well maintained.
To be considered pleomorphic infiltrating lobular carcinoma, Weidner et al. (18,21)
insisted that pleomorphic nuclei be present in at least half of the tumor cells composing
the lesion. Also, if portions of the tumor (more than one low magnification field,
40x) showed alveolar and/or solid areas of invasion, the tumor could not be
considered invasive pleomorphic lobular carcinoma.
The alveolar variant of infiltrating lobular carcinoma consists of cells of the same
uniform appearance as the classical type but they are clustered in small aggregates of
20 or more cells. In the solid variant, the cells are of uniform lobular type but infiltrate
in diffuse sheets with little or no intervening stroma. The tubulolobular variant is
composed of cords of small lobular carcinoma-like cells in collagenous stroma. But,
the cells in some cords form distinct microtubules. These tubules are smaller than
those in tubular carcinoma and the invasive pattern is that of classical invasive lobular
carcinoma. In tubulolobular carcinoma elastosis is often present as are foci of
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