Secondary malignancies diagnosed using kidney needle core biopsies: a clinical and pathological study of 75 cases

Involvement of the kidney by secondary malignancies is uncommon. Differentiating secondary malignancies from primary kidney/urothelial tumors can be challenging, especially on limited biopsy material. A retrospective search of our institutional archive from January 2002 to May 2015 identified 1572 cases of imaging-guided needle core biopsies of the kidney. Of these, 75 (5%) cases revealed a secondary malignancy; 48 (64%) patients had undergone the biopsy with a primary kidney tumor favored clinically. There were 39 male and 36 female patients with a mean age of 59.4 years (range, 21-83 years). The majority of the cases (n = 55, 73%) were metastases from solid tumors, with lung being the most common primary site (n = 22, 29%). Diffuse large B-cell lymphoma was the most common hematological malignancy (n = 6) secondarily involving the kidney. Radiographically, 58 (77%) cases presented as a solitary kidney mass. The primary malignancy was known prior to the kidney biopsy in 66 (88%) cases. The mean interval between diagnoses of the primary tumor and secondary involvement of the kidney was 4.5 years. Immunohistochemical stains were performed in 65 (87%) cases. Follow-up information was available for 73 patients; mean survival was 19.4 months, with 43 patients dead of their disease (mean, 12 months) and 30 patients alive at last follow-up (21 with and 9 without disease; mean, 30 months). Secondary malignancy in the kidney may clinically and pathologically mimic primary kidney tumors. Accurate diagnosis can be rendered by correlating pathological features with clinical and radiographic findings and judicious use of ancillary studies.