**2.1.11 Biological variation of tumour growth**

As defined in the tumour growth situation, the exponential function is added to the steadystate including a biological variation CVB. This exponential function can further be varied by multiplying the concentration due to the exponential function by a random factor times 0.25, which corresponds to an extra biological variation in tumour growth of 25 %.

As previously defined, the tumour growth is expressed as an exponential function: 0.95\*eλt, where λ is the slope and t is the time (days or months). The 25% extra biological variation within the tumour growth is then expressed with:

#### (1 + randomk\*0.25)\*0.95\*eλ<sup>t</sup> ,

where randomk is a new random number from a Gaussian distribution, and the start concentration of tumour growth is still expressed by the factor 0.95, when t = 0, i.e. 1% of cut-off concentration.
