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

low-grade (small-cell-type) duct carcinoma in situ (DCIS), which has a
micropapillary, clinging, and/or cribriform pattern. Necrosis and inflammatory
infiltrates are rare. For a tumor to be considered tubulolobular (and thus have a very
favorable prognosis) Ellis et al. (2) insisted that the tumor display the characteristic
pattern in over 90% of its area.
Invasive carcinomas showing combinations of the various "lobular" patterns are
classified as mixed variant lobular carcinomas. Ellis et al. (2) insisted that a second
pattern had to compose greater than 20% of the tumor to be consider mixed. Also, like
Dixon et al. (6-8), Ellis et al. included in the mixed category those invasive lobular
carcinomas that displayed the classical lobular morphology, but also had areas of
greater cellular atypia and pleomorphism (or features overlapping with ductal NST).
Ellis et al. did not consider a pleomorphic variant of invasive carcinoma, but instead
chose to place "biphasic" tumors, containing less than 90% invasive lobular carcinoma
and greater than 10% ductal NST, into a category of mixed ductal (NST) and lobular
(apparently the remainder were considered as mixed lobular, although it is not entirely
clear from the Ellis et al. paper).
When invasive lobular carcinomas metastasize to lymph nodes, the carcinoma cells
may be distributed largely in sinusoids, sparing lymphoid areas. When lymph node
involvement is sparse, the distinction between tumor cells and histiocytes may be
difficult and reactive changes in histiocytes in the sinusoids of lymph nodes may
resemble metastatic lobular carcinoma. Moreover, the metastatic patterns may mimic
lymphoma. I have seen examples of invasive lobular carcinoma of the breast
associated with a prominent lymphoid component that obscures the “true” diagnosis.
Cytokeratin immunoperoxidase stains usually resolve these problem cases.
The metastatic patterns of lobular carcinoma are different from those of InvDC,NST,
with GI tract, gynecologic system, and peritoneum-retroperitoneum metastases
markedly more prevalent in lobular carcinoma (31). Central nervous system
metastases usually occur as carcinomatous meningitis in the form of diffuse
leptomeningeal infiltration (32,33). Intra-abdominal metastases tend to involve the
serosal surfaces, retroperitoneum (32,34), or ovaries (35). Metastases to the stomach
may closely mimic linitis plastica (36). Diffuse spread to the uterus and ovaries with
ovarian enlargement creates the features of Krukenberg tumor with clinical and
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