Microscopic description:

Dense collection of spindle cells around epithelial components.

Nested cellular pattern with rounded nuclei and centered nucleoli.

IHC: Stained positive for ER, PR, CD117, Ki67 <1%, smooth muscle actin, PAX 8, AE1/AE3; negative for HMB, CAIX.

Based on histopathological feature and IHC stains, it is believed that the mass is oncocytoma in concert with mixed epithelial stromal tumor.

Molecular profile:

Mixed epithelial stromal tumors (MEST) are a rare, mostly benign, biphasic, renal tumor that typically occurs as a unilateral, solitary lesion.

The majority of MEST cases occur in perimenopausal women with an average age of ~52 years old.

Long term estrogen replacement therapy is thought to be a predisposing factor in females.

The stromal and epithelial components are believed to arise from cells of similar origin, as the nonrandom inactivation pattern of the X chromosome is identical.

IHC varies between cases; however, the vast majority of MEST stain positive for ER, PR, SMA, PAX8, and desmin.

References:

Adsay, N. V., Eble, J. N., Srigley, J. R., Jones, E. C., & Grignon, D. J. (2000). Mixed Epithelial and Stromal Tumor of the Kidney. The American Journal of Surgical Pathology, 24(7), 958–970.

Choy, B. (2020, August 9). Mixed epithelial and stromal tumor. https://www.pathologyoutlines.com/topic/kidneytumormixedepithelial.html

GIAMBELLUCA, D., ALBANO, D., GIAMBELLUCA, E., BRUNO, A., PANZUTO, F., AGRUSA, A., DI BUONO, G., CANNIZZARO, F., GAGLIARDO, C., MIDIRI, M., LAGALLA, R., & SALVAGGIO, G. (2017). Renal endometriosis mimicking complicated cysts of kidney: Report of two cases. Il Giornale Di Chirurgia, 38(5), 250–255. https://doi.org/10.11138/gchir/2017.38.5.250

Mohanty, S. K., & Parwani, A. V. (2009). Mixed Epithelial and Stromal Tumors of the Kidney: An Overview. Archives of Pathology & Laboratory Medicine, 133(9), 1483–1486. https://doi.org/10.5858/133.9.1483

Picken, M. M., Bova, D., Pins, M. R., & Quek, M. L. (2018). Mixed Epithelial and Stromal Tumor of the Kidney with Extension into Inferior Vena Cava: Case Report and Discussion of Adult Biphasic Cystic Renal Lesions and the Significance of Vascular Involvement. Case Reports in Pathology, 2018, 8234295. https://doi.org/10.1155/2018/8234295

Picken, M. M., Jones, C. H., & Turk, T. M. T. (2018). Benign Mixed Epithelial and Stromal Tumor of the Kidney With Cytogenetic Alterations—Advances and Controversies in Classification of Biphasic Cystic Renal Tumors. AJSP: Reviews & Reports, 23(1), 44–50. https://doi.org/10.1097/PCR.0000000000000226

Samarakoon, R. T. (2015). Unilateral Renal Cystic Disease: A Case Report of A Rare Disease and Review of Literature. International Journal of Radiology and Imaging Technology, 1(1). https://doi.org/10.23937/2572-3235.1510001

Xie, W.-L., Lian, J.-Y., Li, B., Tian, X.-Y., & Li, Z. (2017). Mixed epithelial and stromal tumor of kidney with renal vein extension: An unusual case report and review of literature. Histology and Histopathology, 32(4), 361–369. https://doi.org/10.14670/HH-11-800

Zheng, S., Yuan, H. C., Liu, L. R., Wei, Q., & Han, P. (2013). Mixed epithelial and stromal tumor of the kidney. The Kaohsiung Journal of Medical Sciences, 29(5), 280–283. https://doi.org/10.1016/j.kjms.2012.09.008

CASE IMAGES