Editors: Francesca Khani ( and Mahmut Akgul (

2021-47/November 22
Contributors: Ali Amin

Female in her late 50s with past medical history of cervical cancer s/p radical surgery and chemoradiation, bilateral hydronephrosis (s/p PCN placement) comes with flank pain. Imaging reveals a 3.0cm solid enhancing right renal mass, suspicious for renal cell carcinoma. Needle biopsy is performed.


1. What is the correct diagnosis?

a. PNET/Ewing sarcoma

b. Mucinous tubular and spindle cell carcinoma

c. Glomus tumor

d. Papillary RCC, solid variant

e. Metastatic poorly differentiated carcinoma (cervix)

Renal glomus tumor

The sections show a monomorphous population of small tumor cells with mild eosinophilic cytoplasm and bland nuclear features, showing sheets and mild perivascular aggregation. Elevated mitotic activity is noted (up to 2/10HPF).

Tumor cells reveal expression of CD99 and SMA, and are negative for PAX8, CK7, CK cocktail, CAIX, CD34, WT1, HMB45, Synaptophysin, DOG1 and Desmin. The morphology and immunophenotype is suggestive of renal glomus tumor.

Glomus tumor is believed to originate from glomus body, and can rarely occur primarily in kidney. The bland tumors cell can form sheets, nests and trabecula in a loose fibromyxoid background. Cells are often round, but fusiform cells can be seen. Immunophenotype shows SMA expression in the absence of cytokeratin and CD34. It is commonly considered a benign entity; however malignant forms have been reported (associated with size>2.0cm, increased mitotic activity with atypical mitosis and marked nuclear atypia. Based on the findings (size and conspicuous mitotic activity), this case is called atypical glomus tumor.

Glomus tumor is a diagnosis of exclusion. PNET/Ewing sarcoma is commonly seen in younger ages, and reveals sheets of small cells with clear cytoplasm, and increased proliferation activity. IHC reveals membranous CD99 expression, positive nuclear FLI1 expression and focal CK and Synaptophysin expressions. Despite expression of CD99 in this case, clinical presentation and expression of SMA makes PNET diagnosis unlikely. MTSC has a characteristic morphology composed of bland cuboidal cells in long cords and tubules in a myxoid stroma, and foci of spindle cells. The tumor cells are positive for PAX8, CK cocktail, CK7 and AMACR, and are negative for smooth muscle markers. Similarly, solid variant of PRCC reveals at least focal papillary configuration, and reveal positive expression of PAX8, CK cocktail, CK7 and AMACR, and are negative for smooth muscle markers. Metastatic poorly differentiated carcinoma, in this case squamous cell carcinoma of the cervix, usually shows high grade nuclear features and PAX8 and CK expressions, and does not reveal muscle marker expression.

Tamboli P, Ro JY, Amin MB, et al. Benign tumors and tumor-like lesions of the adult kidney. Part II: Benign mesenchymal and mixed neoplasms, and tumor-like lesions. Adv Anat Pathol. 2000; 7:47–66.

Al-Ahmadie HA, Yilmaz A, Olgac S, Reuter VE. Glomus tumor of the kidney: a report of 3 cases involving renal parenchyma and review of the literature. Am J Surg Pathol. 2007 Apr;31(4):585-91.

Ali Amin
Brown University/Rhode Island Hospital, RI


Kidney, glomus tumor, SMA.