The impact of location and number of cores on the diagnostic accuracy of renal mass biopsy: an ex vivo study.

OBJECTIVE: To evaluate whether renal mass biopsy (RMB) biopsy location or number affected diagnostic accuracy in a prospective ex vivo study.
METHODS: Three cores (1 central and 2 peripheral) were obtained for histologic processing from each of 48 renal masses after nephrectomy. Individual biopsy cores were evaluated independently for tumor subtype and grade by a single, blinded GU pathologist.
RESULTS: Although individual biopsy cores were informative and confirmed accurate in only 59 % of samples, accuracy increased to 85 % with three-core biopsy (p < 0.01). Cancer identification with a single peripheral core increased to 77 % by adding a central core (p = 0.005), to 80 % with a second peripheral core (p = 0.008), and to 85 % with three cores (p = 0.001). Similarly, diagnostic yield for histologic subtyping increased from 44 % for 1-core biopsy to 59-63 % with 2-core biopsy (p = 0.03) and to 67 % with 3-core biopsy (p = 0.02). The correct subtype was confirmed at nephrectomy for 63 % of clear cell RCC, 60 % of papillary RCC, 100 % of chromophobe RCC and 75 % of oncocytomas. When recorded, nuclear grade corresponded to final grade assignment in 56 % and was within 1 grade in an additional 37 %.
CONCLUSIONS: RMB has not been used routinely in the evaluation of renal cortical neoplasms because of reportedly high rates of indeterminate or inaccurate diagnoses. In this prospective, ex vivo study, single-core RMB results in a low diagnostic yield. Obtaining multiple cores significantly improved diagnostic yield, with similar results with two-core and three-core RMB. We therefore recommend that RMB for suspicion of cancer include at least two peripheral cores.