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

Definitive diagnosis of medullary carcinoma on the needle core biopsy cannot be
made. It is wise to suggest the possibility of this diagnosis and defer the definitive
diagnosis to complete excision of the mass (42).
Lumpectomy and radiation is a therapy for patients with true medullary carcinoma,
espcially for tumors 3 cm or smaller. Sentinal lymph node biopsy is also
recommended for staging. Chemotherapy is usually given to the patients with larger
tumor, positive nodes and tumor with lympovascular emboli (42).
Differential diagnosis: Obviously, the main differential diagnostic problem is
distinguishing between circumscribed and/or “inflamed” examples of InvDC,NST
(i.e., “atypical medullary carcinoma”) from “true” medullary carcinoma. This has
already been discussed above. Other differential considerations include metastatic
tumor to the breast. A metastasis to the breast can be the first sign of a clinically
occult tumor, and its proper diagnosis will lead to a search for the primary and the
avoidance of unnecessary breast surgery. Besides hematolymphoid malignancies (e.g.,
anaplastic large-cell lymphoma), and excluding a metastasis from contralateral breast
carcinoma, most series show that metastatic melanoma and lung carcinoma account
for most cases (greater than 50%) of metastatic disease in the breast (34). Ovarian,
gastric, renal, and pancreatic carcinomas comprise most of the remaining tumor types.
In men, prostate carcinoma has a predilection for metastasizing to the breast (35).
Although it is not likely to be confused with medullary carcinoma, diffuse-type
(signet-ring cell) gastric carcinoma can spread to the breast and mimic invasive
lobular carcinoma (34); likewise, as mentioned above invasive lobular carcinoma can
spread to the stomach and produce linitis plastica (36). Obviously, the distinction
would be very difficult, but immunostaining with GCDFP-15 can help since, like
S100, GCDFP-15 is positive in about 60% of breast carcinomas. (GCDFP-15 and
S100 are also positive in salivary and sweat gland carcinomas, and the melanoma
marker HMB-45 has now been reported to be immunoreactive with breast carcinomas
[37].) Worth to mentioning is that occult breast carcinoma can be diffusely metastatic
to the spleen and present as "idiopathic thrombocytopenic purpura" (38), and that
extra-mammary carcinoid can initially present as a breast mass, simulating primary
breast carcinoma with neuroendocrine differentiation (39). The absence of an in situ
component in the breast should always raise the possibility of a metastatic tumor, but
the presence of an in situ component does not always indicate a breast primary.
Ovarian carcinomas metastatic to the breast can simulate DCIS by growing within the
ducts and lobules and producing microcalcifications mimicking primary carcinoma on
mammogram (40,41). Obtaining a complete clinical history and judicious application
of immunohistochemistry should aid in the proper identification of metastasis to the
breast, thus avoiding unnecessary surgery. Theoretically, rare examples of high-grade
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