On review of the literature, only seven cases of renal mesenchymal chondrosarcoma have been reported. Here we first describe an interesting case of renal mesenchymal chondrosarcoma with a synchronous ureter implant, which was intimately mixed or in collision with an urothelial carcinoma. The biphasic growth pattern of highly cellular undifferentiated tumor cells, with islands of differentiated cartilage is rather characteristic of mesenchymal chondrosarcoma
. Such a distinctive morphology, with the absence of osteoid formation set mesenchymal chondrosarcoma apart from small cell osteosarcoma, Ewing’s sarcoma, dedifferentiated chondrosarcoma, and hemangiopericytoma.
It is important to note that the absence of epithelial component and of an underlying urothelial carcinoma from an extensively sampled tumor, is an indication of pure mesenchymal chondrosarcoma arising from the kidney. The lack of immunoreactivity for epithelial markers, suck as cytokeratin AE1/E3, EMA and E-cadherin lends further support to it. Moreover, the tumor located in the renal parenchyma and distant inferior ureter, not in the calyx and pelvis, the relatively normal collecting system and urothelium that separates the renal tumor and the distal ureteric mesenchymal chondrosarcoma is keeping with the label of tumor implant.
As for the lower ureteric tumor, the transition between the large bulk of mesenchymal chondrosarcoma and the relatively small urothelial carcinoma was abrupt. Moreover, there was no apparent transition between the carcinoma and the ureteric mucosa or epithelium, which is free of dysplasia or neoplastic field changes. Such an observation support a collision of two separate tumors in the lower ureter. There were some reports on a collision of separate tumors in the same location of the urinary system
[9, 10]. While only vascular invasion is observed with mesenchymal chondrosarcoma, and no observed with urothelial carcinoma, such a pattern of metastasis does not necessarily imply that the two malignancies are biologically distinct.
From the view of histogenesis, some groups have proposed that a cell could generate a precursor with greater potential than the cell from which it derives, or transdifferentiation, that allows cell lineage switch. Several such multipotential malignant sarcoma have been reported, for example osteosarcoma and Ewing’s sarcoma with epithelial differentiation
. The primary tumor cell in mesenchymal chondrosarcoma represents a very primitive mesenchymal cell type. Daniel Rubio clearly demonstrated a novel mesenchymal-epithelial transition (MET) associated epithelial tumorigenesis
. And a work showing MET in vitro using a chondrosarcoma tumor cell line has been reported. Fitzgerald MP reported Chondrocytes are mesenchymally derived cells that reportedly acquire some epithelial characteristics, and there is an epigenetic switch associated with an MET-like phenomenon that accompanies chondrosarcoma progression
. These observations support the hypothesis that not all carcinomas are derived from epithelial cells. In our present case, both the urothelial carcinoma and the mesenchymal chondrosarcoma all exhibited polysomy of chromosome 3, 7 and 17, the difference was significant (p < 0.05, chi-square test, SPSS 13.0), and loss of p16 gene by fluorescence in situ hybridization (FISH). The development of urothelial carcinoma had been linked to chromosomal instability, especialy chromosome 3,7and 17 and partial or complete loss of chromosome 9 ( p16 locus)
 . It is thus conceivable that the development of urothelial carcinoma may be triggered or induced by chondrosarcoma, especially since both shared the same clonal origin.
The cytogenetic and molecular mechanism on renal mesenchymal chondrosarcoma is indefinite. Lee AF showed that, in contrast to Ewing sarcoma, small cell osteosarcoma and mesenchymal chondrosarcoma lack FLI-1(Friend leukemia virusintegration-1) immunoreactivity. FLI-1 is therefore useful in the differential diagnosis of small round blue cell tumors of the bone
. Wang L described the novel HEY1-NCOA2() fusion appears to be the defining and diagnostic gene fusion in mesenchymal chondrosarcomas
. Nevertheless, the progression mechanism of renal mesenchymal chondrosarcoma remains to be developed investigated.
The prognosis for mesenchymal chondrosarcoma arising from bone and soft tissue is dismal. Of the seven cases of primary renal mesenchymal chondrosarcoma reported in the English literature, four cases developed local recurrences or metastases at an interval of 1 month to 2.5 years after surgical intervention. In the current case , whether the ureteric tumor represented a direct intraluminal seeding and ‘implant’ ,or a second primary arising from a background with field change remains speculative, but given its highly aggressive nature, it would be tempting to postulate that this highly aggressive tumor shows a propensity for intra-calyxceal spread. The autopsy was not performed, however vascular mesenchymal chondrosarcoma metastasis detected may implicate mesenchymal chondrosarcoma, rather than carcinoma as the lethal metastasis.