Difference between RAT and clear cell papillary renal cell carcinoma/clear renal cell carcinoma

Abstract

We would like to thank Dr. Verine for his interest inour paper on renal angiomyoadenomatous tumors (RAT)[1] and for his letter to the editor [2]. Dr. Verine finds itunfortunate that we did not compare clear cell papillaryrenal cell carcinoma with RAT. In his view, clear cellpapillary renal cell carcinoma shares a lot of similaritieswith RAT, namely CK7, CA-IX, and CD10 immunohisto-chemical positivity and presence of clear cell snouts asshown in the paper of Tickoo et al. [3].We have several cases of clear cell papillary renalcell carcinoma in our files and we must state that thistype of carcinoma is so much different from RAT thatwe did not (and do not) consider it worth listing in thedifferential diagnosis of RAT. Just for mentioning a fewmajor differences between RAT and clear cell papillaryrenal cell carcinoma: RAT is not a papillary tumor at alland is not composed of clear cells either. When presentin RAT, clear cell areas comprise usually only a focalchange. Most of the RAT is usually a basophilic tumorgrowing as a solid lesion, composed of variouslycollapsed tubules. Immunohistochemistry does not playany practical role in the diagnosis of RAT as it sharesan identical immunohistochemical profile with severalentities (it is beyond the scope of this letter to discussthis matter in detail). The immunohistochemistry ofRATs was described in our paper [1]onlytocompletethe pathological features of this distinct entity. We furtherdo not see any similarity between the clear snouts of RATand those illustrated in the paper of Tickoo et al. [3]assuggested by Dr. Verine.Taking further into account the facts that RAT, incontrast to the cases of Tickoo et al. [3], has a typicalangioleiomyomatous stroma, typical capillary vascularity,and lacks the end-stage kidney background, we think thatthe difference between RAT and clear cell papillary renalcell carcinoma/clear renal cell carcinoma is like thatbetween the day and the night or like that between a ratand a hedgehog.In closing, we thank again Dr. Verine for his comments.References