The study by Mary M. Tomayko and C. Patrick Reynolds evaluates the accuracy of various formulas used to determine the size of subcutaneous tumors in athymic (nude) mice, which are a useful model for studying human tumors in vivo. The authors compared 19 different formulas for calculating tumor area, diameter, and volume with the actual weights of 50 tumors ranging from 0.46 to 22.0 g. They found that ellipsoid volume formulas (π/6 × L × W × H and ½ × L × W × H) were the most accurate for estimating tumor mass (r = 0.93), while diameter measurements correlated poorly with tumor mass (r < 0.66). Although tumor area correlated well with tumor mass in small tumors (r = 0.89), this correlation was poor for large tumors (r = 0.41). The study concludes that using ellipsoid volume formulas from measurements of three axes consistently yields the most accurate estimations of both relative and actual tumor mass.The study by Mary M. Tomayko and C. Patrick Reynolds evaluates the accuracy of various formulas used to determine the size of subcutaneous tumors in athymic (nude) mice, which are a useful model for studying human tumors in vivo. The authors compared 19 different formulas for calculating tumor area, diameter, and volume with the actual weights of 50 tumors ranging from 0.46 to 22.0 g. They found that ellipsoid volume formulas (π/6 × L × W × H and ½ × L × W × H) were the most accurate for estimating tumor mass (r = 0.93), while diameter measurements correlated poorly with tumor mass (r < 0.66). Although tumor area correlated well with tumor mass in small tumors (r = 0.89), this correlation was poor for large tumors (r = 0.41). The study concludes that using ellipsoid volume formulas from measurements of three axes consistently yields the most accurate estimations of both relative and actual tumor mass.