Simple method for quantifying pulmonary metastases in a murine fibrosarcoma

A simple method is described for quantitating pulmonary metastases in C57BL/6J mice implanted with the Lewis T241 fibrosarcoma. Lungs were removed from tumor-bearing mice, homogenized, and diluted to 14 ml with supplemented Roswell Park Memorial Institute Tissue Culture Medium 1640 (+5% fetal calf serum). Twenty-five microliters of lung suspension from individual mice were added to a flat-bottomed microtiter plate containing 175 microliters of supplemented media, pulsed with [3H]thymidine, and incubated for 20 hr at 37 degrees. The cells were processed with a multiple automated sample harvester and counted in a liquid scintillator. Total lung burden was extrapolated from measured radioactivity (as cpm) through the use of a standard curve. This method is reasonably accurate and precise and provides more quantitative information on the pulmonary metastatic process than most conventional assays.