Mucinous tubular and spindle cell carcinoma is a rare and only recently described tumour. Only 46 cases have been reported.1
This tumour is seen in adults, predominantly in women, and is typically detected as an asymptomatic renal mass.2
Grossly, mucinous tubular and spindle cell carcinoma is usually well circumscribed with a solid grey to white appearance to the cut surface.2
Histologically, the tumour is composed of cuboidal cells arranged in microtubules and long cords making abrupt transitions to spindle morphology.2
These structures are arrayed in a mucinous or myxoid stroma that reacts strongly with alcian blue.2
Nuclear atypia and mitoses are rare in both cuboidal and spindle cells. Because of the presence of compact tubular architecture, focal papillations and mucin production, the mucinous tubular and spindle cell carcinoma has some morphological similarities with papillary renal cell carcinoma, particularly type 1,2
but extracellular mucin is rare or absent in the latter.
This tumour can also be confused with the papillary renal cell carcinoma that has sarcomatoid change, but in the mucinous tubular and spindle cell carcinoma, spindle cells are arranged in parallel bundles with eosinophilic cytoplasm and low-grade nuclei.3
Immunohistochemistry is not helpful in discriminating between papillary renal cell carcinoma and mucinous tubular and spindle cell carcinoma. The morphological interpretation is still important in the distinction between these tumours.
In summary, mucinous tubular and spindle cell carcinoma is a rare and only recently described distinctive subtype of renal cell carcinoma. It must be differentiated from papillary renal cell carcinoma, especially that with sarcomatoid change, which has a much poorer prognosis.