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

secondary peripheral tumor nodules responsible for the grossly nodular appearance of
medullary carcinomas. The inflammatory infiltrate may be almost entirely of
lymphocytes or plasma cells, but usually there is a mixture. IgG-bearing plasma cells
and peripheral T-lymphocytes predominate in both medullary carcinomas and in
InvDC,NST (20-22,23,24). When plasma cells predominant, the tumor is more likely
to be medullary carcinoma (42).
Circumscription is defined by the border of the infiltrating carcinoma, not by the
periphery of the surrounding lymphoplasmacytic reaction. The tumor cell edges
should have a smooth, rounded contour that pushes aside, rather than infiltrates, the
breast. Consequently, glandular and/or fatty breast tissue should not be found within
the invasive portion of the tumor. If most of the tumor growth (i.e., 75% or more) is
arranged in broad irregular sheets or islands, the pattern is considered “syncytial” and
resembles a poorly differentiated squamous carcinoma. Some have reported that
overall and relapse-free survivals are related to the size of the syncytial component,
with a poorer prognosis associated with a less than 75% syncytial pattern (25).
According to Rosen et al. (26), a tumor that is otherwise characteristic may be
accepted as a medullary carcinoma, even if it has minor components of trabecular,
glandular, alveolar, or papillary growth. Focal metaplastic changes occur in a minority
of medullary carcinomas. Squamous metaplasia, often with necrosis, has been found
in 16%, (10), while osseous, cartilaginous, and spindle cell metaplasia are much less
common. Atypical epithelial giant cells are sometimes seen in the tumor, which also
could be a representative of metaplasia or degenerative changes (42).
Criteria for diagnosing “atypical medullary carcinoma” also seem to vary. Indeed, the
diagnosis may be even more difficult to reproduce between pathologists. According
the Rosen et al. (26) structural variations that characterize atypical medullary carcinoma
include focal invasive growth at the periphery of the tumor, diminished
lymphoplasmacytic reaction, well-differentiated nuclear cytology, few mitoses,
conspicuous glandular or papillary growth, and a less than 75% syncytial growth
pattern. He even suggest calling these tumors as invasvie duct carcinoma with
medullary features (42). Tumors with more than two of these aberrant features are best
classified as infiltrating duct carcinomas (26,10,11). The outcome for patients with
atypical medullary carcinoma may be slightly better than for those with infiltrating
duct carcinoma, but the difference is often not statistically significant. It is also
interesting that in comparison to poorly differentiated duct carcinoma of no special
type, invasvie duct carcinoma with medullary features show the basal-like
immunophenotype more commonly (62.9% vs. 18.9%) (43)
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