Rosen's Breast Pathology, 4e

909

Unusual Clinical Presentation of Carcinoma

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.

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

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

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.