An 80-year-old man presented with hematuria and pain in the left flank.
Puerpercussion in left renal fossa was positive.
Median imaging techniques showed a mass at the level of the left renal fossa that disguised the renal silhouette.
The patient underwent surgery with proximal nephrectomy.
In the nephrectomy specimen, the renal parenchyma was replaced in its entirety by a heterogeneous whitish lesion in which cystic cavities of necrotic appearance combined with hemorrhagic foulish formations could be observed.
Upon cutting, a firm consistency was observed, mainly with the white areas corresponding to cracksaceas, although in other locations a soft consistency was observed, even crux.
The histological study showed a neoplasm consisting of a proliferation of spindle cells and polygonal cells marked with atypical nuclear pleomorphism, adopting a solid growth pattern.
More than 75% of it showed differentiation to osteochondroma and chondrosarcoma, although we could also demonstrate scaly differentiation, mainly covering the internal surface of the cystic formations previously described.
The high cellular atypia observed became more evident with the presence of abundant multinucleated giant cells located within the solid fusiform areas and around the osteosarcomatous differentiation areas are atypical (14).
The tumor contacted the renal capsule without exceeding it, establishing vascular structures of the hilium and adipose tissue of the pelvis.
After rigorous sampling of the surgical specimen, few foci with histological pattern of clear cell carcinoma could be observed.
The immunohistochemical study of the neoplasia showed positive immunostaining for cytokeratins both in the clear cell component and in the fusocellular being the latter equally positive for vimentin (13).
With all this the diagnosis of renal sarcomatoid carcinoma was emitted with predominance of areas with heterologous malignant differentiation (osteo and chondrosarcoma), referring to the presence of foci of carcinoma with clear cell pattern.
