Inter-tumour variability within the same animal. A) The mean IFP value (mmHg) for each individual mammary gland tumour arising in four different MMTV-PyMT transgenic mice is shown. The bar represents the median IFP value (mmHg) for each mouse. There was substantial variation between different tumours within the same mouse. B) The mean IFP value (mmHg) for each of two orthotopic MMTV-PyMT tumours, one transplanted into the left and one into the right 4th mammary gland, is shown. The tumours from the same donor animal are connected by a solid line. Again, there was obvious variation in the IFP values of different tumours growing within the same animal. C) Recipient tumour IFP (mmHg; y-axis) plotted as a function of the mean donor IFP (mmHg; x-axis). The line of identity is shown. There was no correlation between donor and recipient IFP. D) The difference in the mean IFP values of two different tumours growing in the left and the right mammary glands is shown, grouped according to whether the two tumours were initiated from the same or different donor tumours. The median IFP for each group is indicated; there was no significant difference (Mann Whitney test p ≥ 0.05). E) The mean tumour IFP is shown for each individual MMTV-PyMT mammary gland tumour transplanted into either SCID or FVB mouse backgrounds. The bar indicates the median IFP values. The IFP values were comparable for both mouse backgrounds.