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