Metastatic melanoma - kidney (pathology)
History of removal of melanoma on forehead with multiple recurrences. Now presents with flank pain.
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Coronal section of the right kidney ('bi-valved') with relatively circumscribed, firm, pale tan to grey tumor, 68 x 48 x 48mm, in the mid-cortex. The tumor distorts the capsule but does not breach it and does not involve the perinephric fat.
Micro (medium power): The tumor is relatively undifferentiated and was initially labeled a 'malignant spindled cell tumor' favoring metastatic melanoma (given the strong family history).
Micro (high power): The spindled cells show no residual differentiation, including no evidence of residual cytoplasmic pigmentation.
Tumors such as this, with no morphological clues to indicate the cell lineage, are often initially labeled as 'malignant spindled cell tumor'; examples of what a pathologist looks for include residual gland, mucin or keratin production (poorly differentiated carcinoma), melanin pigmentation (melanoma) or specific mesenchymal differentiation (e.g. rhabdomyoblasts, lipoblasts). When these morphological clues are not present, we attempt to uncover residual protein expression (immunohistochemistry), utilize cytogenetic profiling, or sometimes even resort to ultrastructural morphology (electron microscopy). In this case, the immunohistochemical tests confirmed metastatic melanoma.