Figure 2. Wave-front profiles of the tumour-host interface generated from computer simulations and analytic solutions of coupled partial differential equations used to model the acid-mediated tumour invasion hypothesis. Details of this analysis are available in reference [158]. The wave-fronts are propagating left to right with a speed of about 0.03 mm day^–1. Normal tissue is identified as 1 with the boundary of normal cells receding before the advancing wave-fronts of propagating tumour, identified as 2, and the accompanying acid gradient, identified as . Note the predicted acellular gap between the edges of the tumour and normal tissue. The mathematical models predict this gap will occur under some conditions as a result of rapid death of normal cells in the region of most severe extracellular acidosis.