The response to 5-FU treatment can be captured with the combined Gompertz/two-compartment pharmacokinetic model: Indicative figures from two treated mice, one from each treatment group.

<p>Left panel–CM.41 from 5-FU 1; Right panel–CM.43 from 5-FU 2. The black squares indicate the measured tumor volumes while the green line is the fitted model based on Eqs (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0143840#pone.0143840.e002" target="_blank">2</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0143840#pone.0143840.e005" target="_blank">5</a>). The red dashed line is the prediction of what would have happened if the tumor was left untreated based on the pre-treatment data estimates of the tumor growth rate. Our model appears to accurately capture, both the growth and treatment dynamics of the tumor. The NMSE values for the three tumors of CM.41 are 44.7%, 26.8% and 35.4% and for the three tumors of CM.43 these are 18.5%, 6.7% and 13.0% respectively.