Cystic fibroepithelioma of Pinkus: two new cases and cystic changes in classical fibroepithelioma of Pinkus.

We report two new cases of cystic fibroepithelioma of Pinkus together with immunohistochemical features and analyze the presence of cystic changes in a series of 16 classical fibroepitheliomas of Pinkus. Our findings show that the formation of cystic spaces is most probably caused by ischemic degeneration of stromal fenestrations, rather than by central tumor cell necrosis. This finding is supported by lack of CD34 positive blood vessels in edematous and hyalinized stromal fenestrations undergoing transformation into cystic spaces, as opposed to the uninvolved stromal fenestrations. Therefore, it is probably more accurate to refer to this process as pseudocystic stromal degeneration rather than true cyst formation. Also, two out of 16 classical Pinkus fibroepitheliomas exhibited focal pseudocystic changes in 50% and 10% of the tumor, respectively, demonstrating that this degenerative process can be found, rarely and focally, in classical cases as well.