*3.9. Clear Cells*

Only single cases and a short series of 10 cases [75] of clear cell UC have been published so far. An advanced stage at diagnosis and an aggressive clinical course is the rule in these patients. Clear cell change, however, is regularly mentioned in several papers reviewing the varied morphology of UC in the bladder and upper urinary tract [76–80].

Clear cell change in UC reflects intracytoplasmic glycogen accumulation that in some cases is extreme this way resembling the typical clear cells observed in clear cell renal cell carcinoma. Usually, clear cell nests are intermingled in the tumor with conventional transitional cells (Figure 2g), which makes its correct identification easier. However, if the clear cell change is generalized or if transurethral resection specimens do not contain pieces of evidence of the urothelial origin of the tumor, the possibility of metastasis in the bladder of a clear cell renal cell carcinoma should be always taken into account [81].
