Mucinous tubular and spindle cell carcinoma of kidney: A case report of a mucin and stroma poor tumour causing diagnostic difficulty

Mucinous tubular and spindle cell carcinoma (MTSCC) is a rare and unusual variant of renal cell carcinoma (RCC). We report an unusual tumour in an 81-year-old male with an incidental finding of a tumour in the lower pole of the left kidney. The core biopsy showed a renal cell carcinoma with mostly tubular morphology and an immunophenotype indistinguishable from papillary renal cell carcinoma. The partial nephrectomy showed a tumour comprising predominantly tubular structures with focal abortive papillae, psammomatous calcifications and scattered small aggregates of foam cells. Only focal areas showed myxoid change and spindle cells, but this made the diagnosis of a mucinous tubular and spindle cell carcinoma more straightforward. This case highlights the importance of recognising a mucin/stroma poor variant of MTSCC of the kidney and how the entity can cause diagnostic confusion with papillary renal cell carcinoma as there is morphologic and immunophenotypic overlap, particularly on core biopsy.