Chemosensitivity testing of small biopsy specimens

Chemosensitivity testing has usually been limited to tumor specimens of 2–3 g or more. We evaluated the miniaturized, improved nucleic acid precursor incorporation assay (MINI‐assay) in 100 small biopsy specimens of 1 g or less. Tumor types included malignant melanomas; sarcomas; and breast, colon, lung, and ovarian carcinomas. Overall, 74/100 were evaluable. The evaluability rate was related to size: 41/48 (85%) 0.7–1.0‐g specimens were evaluable, as opposed to 22/35 (64%) 0.4–0.6‐g and 11/17 (64%) 0.1–0.3‐g specimens. Evaluability was not correlated with tumor types or whether the tumor was from a primary or metastatic site, but was related to yield of viable tumor cells. No viable tumor cells were obtained in 17 specimens, and thus no assay was performed. When 105 cells per well were plated, 49/54 (91%) assays were evaluable, but only 25/29 (86%) were successful when fewer cells were used. Four or more anticancer drugs could be tested in 69/74 (95%) of the evaluable assays. Yielding high evaluability rates and requiring fewer viable cells, the MINI‐assay has allowed us to perform chemosensitivity tests on previously unusable biopsy specimens.