Lu, ZhichunAl-Obaidy, KhaleelCheng, LiangPerry, Kyle D.Grignon, David J.Williamson, Sean R.2018-09-142018-09-142018Lu, Z., Al-Obaidy, K., Cheng, L., Perry, K. D., Grignon, D. J., & Williamson, S. R. (2018). Immunohistochemical characteristics of Renomedullary interstitial cell tumor: a study of 41 tumors with emphasis on differential diagnosis of mesenchymal neoplasms. Human Pathology. https://doi.org/10.1016/j.humpath.2018.07.010https://hdl.handle.net/1805/17309Renomedullary interstitial cell tumors (RMICT) are almost always incidentally identified either at autopsy or resection of the kidney for other reasons. However, rare cases have been reported which are large, resulting in a clinical mass. The immunohistochemical phenotype of usual, incidental RMICT using modern soft tissue tumor markers in is largely unknown, however, providing little information to aid in classification of larger or atypical tumors. We retrieved 41 RMICTs from 36 patients, and studied pathologic characteristics including morphology, immunohistochemistry (S100, keratin AE1/AE3, smooth muscle actin, desmin, estrogen and progesterone receptors, calponin, CD34, CD35), and histochemical staining. Data collected included age, gender, tumor size, laterality, and indication for kidney examination. RMICTs (n = 41) were identified in 23 men and 13 women, with mean age 57 years (range 24–83), tumor sizes ranged from <1 to 13 mm (median 4 mm). Kidneys were resected for 32 tumors, 1 chronic pyelonephritis, 1 trauma, and 2 autopsies. All (41, 100%) had entrapped renal tubules, 5 (12%) of which included cystic or dilated tubules. Most (35, 85%) had collagenous fibers, all of which were negative for Congo red. RMICT demonstrates a largely negative immunohistochemical phenotype with weak to moderate labeling for smooth muscle actin and calponin that is substantially less than myofibroblastic lesions. Positive staining for estrogen and progesterone receptor is common (61%), which could overlap with mixed epithelial and stromal tumor and other entities; however, staining is typically weak. CD34 is usually negative, with occasional weak labeling, in contrast to solitary fibrous tumor.enPublisher Policyrenomedullary interstitial cell tumorkidneyrenal mesenchymal tumorsArticle