Unusual Clinical Presentation of Carcinoma
909
sections of a mass of matted lymph nodes may be required
to find a portion of uninvolved lymph node. The specimen
should be examined for axillary breast tissue (see following
discussion of Carcinoma in Ectopic Breast Tissue). An un
usual, largely hypothetical, source for mammary carcinoma
arising in the axilla is ectopic breast tissue in an ALN.
164,165
This phenomenon is not likely to be recognized in a case
presenting with an enlarged lymph node, because the het
erotopic tissue will probably have been overgrown by the
carcinoma.
The distinction between medullary carcinoma and met
astatic carcinoma in a lymph node can be a particularly
vexing problem. A reticulin stain is useful in this situa
tion to reveal the underlying architecture of ducts that may
be present in a primary carcinoma or the structure of a
membrane antigen (EMA), S-100 protein, carcinoembry
onic antigen (CEA), lymphoid markers, and other mark
ers usually resolve the differential diagnosis. Mammary
carcinoma is typically immunoreactive for CK7 but not
for CK20. Absence of reactivity for E-cadherin is helpful
for identifying metastatic lobular carcinoma. In current
practice, it is almost never necessary to employ electron
microscopy.
163
When adenocarcinoma has been diagnosed in tissue re
moved from an axillary mass, there may be uncertainty as
to whether this represents a metastasis or a primary axil
lary tumor. Because this distinction cannot be made reliably
on the basis of a needle biopsy sample, excisional biopsy is
essential. Variation in the characteristics of tumor among
affected lymph nodes can be helpful for diagnosis. Several
FIG. 33.14.
Occult carcinoma, clear cell.
A:
This metastatic carcinoma in an ALN was the initial
manifestation of breast carcinoma in this patient.
B:
A clinically unapparent focus of intraductal
carcinoma, clear cell type, with a surrounding lymphocytic reaction was found in the breast.
FIG. 33.15.
Occult carcinoma, diffuse.
A:
The patient presented with this enlarged ALN found to
contain malignant cells diffusely infiltrating the lymphoid tissue. The tumor cells were immunore-
active for cytokeratin (
not shown here
).
B:
Poorly differentiated infiltrating ductal carcinoma found
in the breast.
