GAP43 and neoplasm: In line with the GAP43 expression patterns, quantification of the tumour microtube area per cell identified significantly larger tumour microtube areas per cell in the untreated relapsed PDX as compared to the matched untreated primary PDX tumours, and also showed a decrease in the tumour microtubes at the minimal residual disease stage and an increase in the regrown tumours (Fig. 7D).