Collagen ultrastructure in high mammographic density breast tissue. This image won the BCR/BCN image competition. This topographical map was generated by atomic force microscopy (AFM) of peri-ductal breast tissue taken from an individual with high mammographic density. The area of highest density was biopsied from the breast guided by mammography and the biopsy cryosectioned for AFM imaging. The map measures 150?×?150 µm and the AFM tip sampled the surface of the section at a frequency of 4992?×?4992 for an effective resolution of 30 nm per pixel. The sampling rate was 0.0001 Hz and as such each line took 12 minutes to collect; the whole map took 16 hours. Large collagen fibril bundles (fibres) can be observed connected to the surrounding tissue by a network of fine fibrils (150–450 nm diameter). Such fibres were not observed in matched low mammographic density breast tissue. These findings are of interest in the context of breast cancer development given that increased collagen organisation is strongly linked to raised tissue stiffness. Concomitantly, tumour cells are known to prefer a stiff matrix. As such increased collagen organisation may be a mediator of mammographic density and therefore cancer risk. From the work of Dr James McConnell, University of Manchester.