Tissue Microarrays from Renal Cell Tumors: Exclusion Criteria and Rate of Exclusion

Objectives: Exclusion of tissue microarray (TMA) cores can cause the total loss of a tumor case, and this can have a potentially negative effect on the results of TMA-based studies. The main aim of this study was to evaluate the loss of informative cores having cut a given number of slices from a TMA block. A further objective was to investigate the effect in various subtypes of renal cell tumors and the detailed reasons for the loss of informative cores.

Material And Methods: A TMA was constructed from renal tumor specimens (n=461). The cause and rate of exclusion were evaluated in the first slice (FS) and last slice (LS) (i.e. the 40th) cut from the TMA blocks. Furthermore, the overall case loss under the assumptions that only one, two or three cores per case were punched was extrapolated.

Results: Sarcomatoid and papillary renal cell carcinomas showed the highest overall exclusion rate. Irrespective of the type of tumor, however, the case loss was approximately tripled from FS to LS. Furthermore, extrapolation showed that a reduction in the number of cores punched per case, for example by one, would further double the number of cases lost. Reasons for exclusion were mainly as follows: core loss; <25% tumorous tissue per core; core folding; and core with necrotic area.

Conclusion: This study shows that punching at least three to four cores per case is advisable when constructing TMAs from oncocytoma and renal cell carcinoma specimens, and that the type of tumor has an effect on the cause and rate of core exclusion.