Mucinous, tubular and spindle cell carcinoma of kidney: report of two cases with pathological differences.

Objective: To describe two cases of a rare type of renal tumor , mucinous tubular and spindle cell carcinoma (MTSC), with different pathologic features.
Methods: We present: 1) the case of a 36 year-old woman 24-week pregnant, in whom during an examination for a renal colic we discovered a 5.5 cm tumor in the lower pole of the left kidney. 2) A 71-year-old woman that consulted to her doctor due to loss of weight (5 kg) and anorexia. A 15 x 12 x 9.5 cm tumor was found in her left kidney.
Results: Radical nephrectomy was performed in both cases. Microscopic examination showed a myxoid matrix containing a proliferation of tubules and spindle cells, with low-grade atypia. Cells were immunoreactive for CK7, racemase, EMA and vimentin and negative for CD10. Case 1 had some foci of papillary morphology, and was pT1. Case 2 had some nests of clear cells and invaded the sinus fat focally. It was staged as pT3a. In April 2012, the patients are alive without evidence of recurrence or metastasis after 13.5 years (case 1) and 8 months (case 2) of follow up.
Conclusions: MTSC is a rare type of renal carcinoma, which can appear with different clinical, gross and microscopic features. This tumor seems to share some morphological and immunohistochemical similarities with renal papillary carcinoma, and the differential diagnosis is difficult. The vast majority of cases reported had favourable evolution, like our case 1, although a remote possibility of metastasis exists, in cases with sarcomatoid differentiation, but even without it.