[480] Defining Histopathologic Criteria of Cutaneous Metastatic Melanomas: A Clinicopathologic Study of 160 Cases with Emphasis on the Morphologic Spectrum

JA Plaza, C Torres-Cabala, H Evans, H Diwan, VG Prieto. Medical College of Wisconsin, Milwaukee, WI; MD Anderson Cancer Center, Houston, TX

Background: Metastatic melanoma is a common source of cutaneous metastasis. In up to 5% of patients, cutaneous metastasis can be the first manifestation of melanoma. The diagnosis of metastatic melanoma usually poses little diagnostic difficulty, but occasionally it can adopt unusual or unfamiliar appearances mimicking benign and malignant neoplasms (spindle cell carcinomas, atypical fibroxanthomas, blue nevi, dermatofibromas, leimoysarcomas, etc). In this study, we present 160 cases of cutaneous metastatic melanomas and thoroughly analyze their histomorphologic spectrum. To the best of our knowledge this is the largest series of cutaneous metastatic melanomas.
Design: 160 cases with metastatic melanoma to the skin were the basis of our study. Glass slides stained with H&E for each case were reviewed. Paraffin blocks or unstained slides were available for immunohistochemical studies in all cases. Metastases to areas with important drainage of lymph node such as axillary region or groin, or histological evidence of lymph node remnants were criteria for exclusion from the study. Direct extension from lymph nodes was also excluded.
Results: Cases were classified by anatomic site of metastasis, primary origin, age and sex. The patients were 97 men and 63 women ranging from 51 to 88 years (mean 69.5). The tumors were located in back, upper extremities, lower extremities, abdomen, and head and neck area. The tumors ranged in size from 0.8 cm to 3.0 cm. The majority of metastatic melanomas showed classic histomorphologic appearance. In up 21.6% of cases, the lesions mimicked blue nevus, dermatofibroma, metastatic carcinoma, malignant and benign vascular neoplasms, and smooth muscle neoplasms. In such cases, immunohistochemical studies were used to aid the diagnosis. All metastatic melanomas had high proliferative rate (with MIB-1) and patchy expression of HMB45 antigen.
Conclusions: The histologic diagnosis of cutaneous metastatic melanoma can pose difficulties for diagnosis, especially if there is an unknown primary neoplasm, requiring ancillary studies and reliable histomorphologic criteria to establish an accurate diagnosis.
Category: Dermatopathology

Wednesday, March 11, 2009 9:30 AM

Poster Session V # 39, Wednesday Morning