Cystic nephroma and mixed epithelial and stromal tumour of the kidney: opposite ends of the spectrum of the same entity?
OBJECTIVE
The term "renal epithelial and stromal tumour" (REST) was proposed recently to encompass the spectrum of findings observed in cystic nephroma (CN) and mixed epithelial and stromal tumour (MEST) of the kidney. Our aim was to review the broad spectrum of usual and unusual clinical and morphologic findings observed in CN and MEST.


METHODS
Based on Medline database searches, all aspects of CN and MEST were assessed.


RESULTS
CN and MEST have a remarkable similarity in sex predilection, age distribution, and morphologic attributes of both the epithelial and stromal components and immunohistochemical profile, albeit with variation in individual categories, with higher prevalence of stromal-to-epithelial ratio, prominent ovarian-like stroma, smaller cysts, and stromal luteinisation in MEST, and large cysts, thin septa, and low stromal-to-epithelial ratio in CN. The stromal component in both lesions expresses estrogen and progesterone receptors. Rare and unusual morphologic features, such as endometrioid, cervical, and intestinal differentiation, and luteinised ovarian-like stroma, have been described in MEST. The epithelial element occasionally shows estrogen and progesterone receptors. Rare aggressive behaviour has been reported for both neoplasms.


CONCLUSIONS
Considerable overlap is apparent between the two lesions, which suggests that they may represent opposite ends of the spectrum of the same process. Even though an aggressive behaviour has been reported in very few cases, in general both neoplasms are considered benign and surgical excision is curative.
Montironi
Rodolfo
R
Section of Pathological Anatomy, Polytechnic University of the Marche Region, School of Medicine, United Hospitals, Ancona, Italy. r.montironi@univpm.it
Mazzucchelli
Roberta
R
Lopez-Beltran
Antonio
A
Martignoni
Guido
G
Cheng
Liang
L
Montorsi
Francesco
F
Scarpelli
Marina
M
D006801:Humans; D007680:Kidney Neoplasms / Q000145:classification* / Q000473:pathology*