Rapid in vitro assay for predicting response to fluorouracil in patients with metastatic breast cancer.

PURPOSE To determine if a rapid 3H-uridine uptake assay using breast tumor cells from biopsy specimens could predict clinical response to fluorouracil (5FU) in patients with metastatic breast cancer. PATIENTS AND METHODS A double-blind prospective study was conducted of 60 patients with measurable, metastatic breast cancer who had failed to respond to at least one prior chemotherapy regimen. Patients received 5FU 300 mg/m2/d by continuous infusion and were monitored for response. Tumor cells from biopsy specimens were grown in microwells and exposed for 3 days to 0.1, 1.0, 10.0, and 100.00 micrograms/mL of 5FU on strips coated with drug and extracellular matrix. Cells were pulsed with 3H-uridine overnight. Incorporated radioactivity was compared for wells with and without drug. Results were available 4 days from specimen submission. RESULTS Of 45 eligible patients, 11 (24%) were not assessable in vitro. Nine patients were assessable in vitro, but not clinically. Of the remaining 25 patients, who were assessable both clinically and in vitro, there was one complete response (CR), five partial responses (PRs), five cases of stable disease, and 14 cases of progressive disease, for an objective response rate of 24%. Response in vitro was significantly correlated with clinical response (P = .002). Of six clinical responders, five also responded in vitro, for an assay sensitivity of 83%. Of 19 nonresponders, 17 were nonresponders in vitro, for a specificity of 89%. The positive predictive value of the test was 71% (five of seven), and the negative predictive value was 94% (17 of 18). CONCLUSION Results of an in vitro assay were significantly correlated with clinical response in patients with metastatic breast cancer treated with continuous infusion 5FU.