Renal cell carcinoma and the clonogenic assay.

The clonogenic assay is an in vitro chemosensitivity test performed on tumor specimens and has had limited success in predicting or confirming patient response to chemotherapy. We investigated this assay system, using a 1-hour method, in 37 renal cell carcinoma specimens to determine its clinical usefulness. These specimens also were graded independently by a pathologist with respect to cell type, mitotic figures and degree of differentiation. Only 22 specimens formed at least 50 colonies per 500,000 cells plated and few specimens displayed any chemosensitivities. Marked variations of colony counts among duplicate controls or drug-treated samples demonstrated further the unreliability of the assay. Of several factors responsible for the poor performance of the assay the 2 outstanding problems were losses of clear cells in variable amounts (unique to renal cell carcinoma), and the inability to generate and maintain single cell suspensions. Pathologic correlations confirmed that predominantly clear cell carcinomas did not form colonies as well as granular cell carcinomas. Owing to these problems in its present form the clonogenic assay is not useful clinically and is unsuited particularly for renal cell carcinoma.