Low-grade Oncocytic Tumor of Kidney (CD117 Negative, Cytokeratin 7 Positive): A Distinct Entity?

Abstract

Aim To describe a group of distinct low‐grade oncocytic renal tumors that demonstrate CD117 negative/Cytokeratin (CK) 7 positive immunoprofile.

Methods and results We identified 28 such tumors from 4 large renal tumor archives. We performed immunohistochemistry for: CK7, CD117, PAX8, CD10, AMACR, e‐cadherin, CK20, CA9, AE1/AE3, vimentin, BerEP4, MOC31, CK5/6, p63, HMB45, melan A, CD15 and FH. In 14 cases we performed array CGH; in 9 cases with successful result. Median patient age was 66 years (range 49‐78 years) with a male‐to‐female ratio of 1:1.8. Median tumor size was 3 cm (range 1.1‐13.5 cm). All were single tumors, solid and tan‐brown, without a syndromic association. On microscopy, all cases showed solid and compact nested growth. There were frequent areas of edematous stroma with loosely arranged cells. The tumor cells had oncocytic cytoplasm with uniformly round to oval nuclei, but without significant irregularities, and showed only focal perinuclear halos. Negative CD117 and positive CK7 reactivity were present in all cases (in 2 cases there was focal and very weak CD117 reactivity). Uniform reactivity was found for: PAX8, AE1/AE3, e‐cadherin, BerEP4 and MOC31. Negative stains included: CA9, CK20, vimentin, CK5/6, p63, HMB45, Melan A and CD15. CD10 and AMACR were either negative or focally positive; FH was retained. On array CGH, there were frequent deletions at 19p13.3 (7/9), 1p36.33 (5/9) and 19q13.11 (4/9); disomic status was found in 2/9 cases. On follow‐up (mean 31.8 months, range 1‐118), all patients were alive with no disease progression.

Conclusion Low‐grade oncocytic tumors that are CD117 negative/CK7positive demonstrate consistent and readily recognizable morphology, immunoprofile, and indolent behavior.