Heterotopic breast tissue versus occult metastatic carcinoma in lymph node, a diagnostic dilemma.

Breast cancer is the leading cause of cancer in women and the third leading cause of cancer mortality in the United States. We report a case of a patient who underwent bilateral simple mastectomies and right sentinel node biopsy for invasive lobular carcinoma in the right breast. An ipsilateral sentinel lymph node showed a microscopic focus of ductal elements. Although residual lobular carcinoma was identified in the right breast, no ductal carcinoma was identified in either breast. The ducts were discrete distributed in a 3-mm focus in the lymph node parenchyma as well as the subcapsular sinus. By immunohistochemistry, the ducts were positive for cytokeratin, estrogen receptor/progesterone receptor and did not show a myoepithelial layer by P63 or smooth-muscle myosin heavy-chain staining. The differential diagnosis includes heterotopic epithelial inclusions and benign mechanical transport. Mechanical transport of the breast tissue was ruled out because primary tumor type in the breast and the ductal structures in the lymph nodes were of different types. The diagnosis of occult metastatic tumor was based on the lack of the myoepithelial layers associated with the ductal structures. The diagnostic dilemma of the differential diagnoses is discussed, and pertinent literature is reviewed.

Pathobiology of the sentinel node.

PURPOSE OF REVIEW: Lymphatic mapping and sentinel lymph node biopsy have been established as definitive procedures for the staging of cutaneous melanoma. Large-scale studies that have been recently conducted and that are ongoing suggest a therapeutic role for lymphatic mapping/sentinel node biopsy in the management and prognosis of melanoma patients with early lymph node metastases. RECENT FINDINGS: Sentinel node biopsy has been shown to extend disease free survival and increase melanoma-specific survival for patients with early nodal metastases according to interim analysis of the Multicenter Selective Lymphadenectomy Trial 1 (MSLT-1). The proper evaluation of sentinel lymph nodes requires histologic and immunohistochemical analysis of multiple levels. Immune modulation has been shown to play an important role in nodal metastasis. SUMMARY: There is increasing evidence for the efficacy of lymphatic mapping and sentinel lymph node biopsy in predicting prognosis, reducing the morbidity traditionally associated with regional lymph node dissection and increasing survival in subgroups of patients with cutaneous melanoma. Further study is needed to determine the role of the immune system in the spread of nodal metastases and the role of immunomodulatory therapy to prevent or possibly even reverse nodal metastases.

Immunohistochemical characteristics of melanoma.

Melanoma has a wide spectrum of histologic features which mimic epithelial, hematologic, mesenchymal, and neural tumors. Immunohistochemistry has been the primary tool to distinguish melanomas from these other tumors; it has also been studied for use as an adjunct to distinguish benign and malignant melanocytic tumors and to elucidate prognosis. Furthermore, there has been extensive effort to find a suitable marker to differentiate spindle cell and desmoplastic melanoma from other tumors. We have reviewed the literature investigating melanocytic differentiation markers, proliferation markers, immunomodulatory markers, signaling molecules, and nerve growth factors and receptors. Despite the proliferation of immunohistochemical markers, S-100 remains the most sensitive marker for melanocytic lesions, while markers such as HMB-45, MART-1/Melan-A, tyrosinase, and MITF demonstrate relatively good specificity but not as good sensitivity as S-100. No marker has proven useful in distinguishing spindle cell and desmoplastic melanomas from other tumors. Ki67 remains the most useful adjunct in distinguishing benign from malignant melanocytic tumors. None of the markers reviewed has been shown conclusively to have prognostic value for melanocytic neoplasms.

Pathologic reporting and special diagnostic techniques for melanoma.

Pathologists play a central role in the management of cutaneous melanoma in determining that a tumor is a melanoma, whether or not it is primary or metastatic, and whether or not the margins of excision are tumor free and in evaluating prognostic indicators from examination of the primary tumor and, where appropriate, lymph nodes, including the sentinel nodes.