Clinical history: 52 year old male with incidental renal mass on imaging.
What is the diagnosis?
Mucinous Tubular and Spindle Cell Carcinoma
This is a rare tumour of the kidney, occurring predominantly in females, with a M:F ratio of 1:4. Patients range in age from 13 to 82 years, with a mean age of 53. Although some tumours are symptomatic, the majority are discovered incidentally. Tumours average 6-7 cm in size, are sharply circumscribed, gray-white, tan, or yellow, sometimes with minimal hemorrhage and/or necrosis. Microscopically, they consist of tightly packed, small elongated tubules separated by abundant basophilic extracellular mucin, sometimes with a “bubbly” myxoid appearance. The mucin stains strongly with Alcian blue at pH 2.5. Tubules are lined by uniform low cuboidal cells with scant cytoplasm, and round nuclei of low nuclear grade with absent or inconspicuous nucleoli. Mitotic figures are rare. The histologic spectrum may include cases in which the spindle cell component rivals or even exceeds the tubular component as well as cases with relative paucity of mucinous matrix, aggregates of foamy macrophages, papillations or small components of well formed papillae, focal clear cell change in tubular cells, focal necrosis, oncocytic tubules, numerous small vacuoles, psammomatous calcification, or heterotopic bone formation.
The exact cell of origin of this neoplasm is not well defined. Accumulated evidence suggests that these tumours originate either from cells of the loop of Henle or from collecting duct epithelium, with more support for the latter site. Tumour cells are typically immunoreactive for EMA, keratin AE1/AE3, CK7, CK19, CK903, and AMACR. It has been pointed out that there is considerable overlap between the morphological and immunohistochemical features of mucinous tubular and spindle cell carcinoma and that of papillary renal cell carcinoma, emphasizing the possibility that mucinous tubular and spindle cell carcinoma is simply a variant of papillary renal cell carcinoma. However, despite morphologic and immunohistochemical similarities to papillary renal cell carcinoma in some cases, the gains of chromosomes 7 and 17 and loss of Y chromosome that are characteristic of papillary RCC are not seen in mucinous tubular and spindle cell carcinoma.
These tumour are generally of low pathologic stage at the time of excision, and they behave in an indolent fashion.