Mixed epithelial and stromal tumors of the kidney: evidence for a single cell of origin with capacity for epithelial and stromal differentiation.

Mixed epithelial and stromal tumors are uncommon biphasic tumors of the kidney, with cystic and solid areas composed of a morphologically diverse stroma, including ovarian-like stroma and an epithelial component with considerable heterogeneity. Little is known about the histogenesis and clonal origins of these tumors. A total of 21 mixed epithelial and stromal tumors of the kidney from female patients who underwent radical or partial nephrectomies were examined. The epithelial and stromal components, and also adjacent non-neoplastic renal parenchymal tissues were separately laser microdissected from sections prepared from formalin-fixed and paraffin-embedded tissues for X chromosome inactivation analysis. Nineteen of the 21 tumors were informative. Seven of these informative cases showed random X chromosome inactivation pattern in both epithelial and stromal components of mixed epithelial and stromal tumors of the kidney. Nonrandom inactivation of the X chromosome was found in 12 of 19 informative tumors. The same pattern of nonrandom inactivation of the X chromosome was seen in both epithelial and stromal components in all 12 of the tumors with nonrandom X chromosome inactivation. Our data support the theory that the stroma and epithelium arise from a common cell of origin.