Aim: Renal needle core biopsies for mass lesions are being used frequently in advanced renal cell carcinoma or multipl mass lesions (e.g., primary renal cell carcinoma or metastatic renal mass). The problems and clues of core biopsy interpretation from a pathologist's perspective have not been fully reported. Current study aims to document our experience.

Materials and Methods: Cases with renal needle core biopsies from 2000 to 2008 were retrospectively evaluated and categorized in 9 groups based on histologic pattern: Category 1-Clear cell lesions; Category 2-Eosinophilic granular cell lesions; Category 3-Tubulopapillary lesions; Category 4-Spindle cell lesions; Category 5-Infiltrating tumors; Category 6-Small blue cell tumors; Category 7-Cystic lesions; Category 8-Necrotic and/or fibrohistiocytic lesions; and Category 9-Inadequate materials. Different immunohistochemical stain panels for each category were used.

Results: In this study, 52 core biopsies from 47 cases were evaluated. An adequate sample was obtained in 46 (88%). Renal cell carcinoma (49%) was most common followed by metastatic tumors (15%) lymphoma (9%) and urothelial carcinoma (4%). Benign tumors were identified in 3 cases (6%). 19% of the biopsies were non-diagnostic. Most of the cases need immunohistochemical panels for differential diagnosis. Category 2 and 5 was the most problematic, requiring frequently immunohistochemistry and clinical correlation.

Conclusion: A wide spectrum of neoplasms is encountered and diagnosable by renal needle core biopsy. The above- mentioned categories would facilitate the approach to the biopsy and provide a diagnostic tool. Clinical correlation and contemporary immunohistochemistry work-up is often essential in eosinophilic-granular cell lesions and infiltrating tumors and would allow more accurate diagnosis.