Atypical Renal Cysts: A Morphologic, Immunohistochemical, and Molecular Study

Area of Science:

• Uropathology
• Renal Pathology
• Oncology

Background:

• Standardized nomenclature is lacking for complex renal cysts with multiple cell layers or papillary projections.
• Atypical renal cysts can present as complex lesions or secondary findings in patients with renal masses or chronic kidney disease.

Purpose of the Study:

• To characterize the morphology, immunophenotype, and genetic alterations of atypical renal cysts.
• To determine if these cysts represent precursors to renal cell carcinoma.

Main Methods:

• Retrieved 29 cases of atypical renal cysts from surgical pathology files.
• Performed immunohistochemistry for CK7, AMACR, CAIX, and CD10.
• Conducted fluorescence in situ hybridization for trisomy 7, 17, and 3p deletion.

Main Results:

• Cysts were classified into clear cell, eosinophilic stratified, and eosinophilic papillary types.
• Clear cell cases showed CK7 and CAIX positivity, resembling clear cell papillary renal cell carcinoma.
• Eosinophilic cases showed CK7 positivity with variable staining for AMACR, CD10, or CAIX, aligning with papillary renal cell carcinoma.
• Trisomy 17 (6 cases) and trisomy 7 (4 cases) were the most common genetic alterations; one case had 3p deletion.
• Follow-up in 23 patients showed 20 alive with no evidence of disease, indicating a generally benign clinical course.

Conclusions:

• Atypical renal cysts exhibit heterogeneous morphology and immunoprofiles, with some mimicking established renal tumors.
• The presence of genetic alterations (trisomy 7/17, 3p deletion) suggests a potential precursor role in some cases.
• Based on current data, these lesions should not be diagnosed as carcinoma, though further study is warranted.