Testicular cancer capillary. Transmission electron micrograph (TEM) of a section through a testicular cancer capillary showing basement membrane (blue) abnormalities. The basement membrane is a barrier to tumour cell metastasis, separating the tumour cells from connective tissue and the vascular endothelium (green). Remodelling, or loss of the basement membrane, is required for tumour cells to reach vessels, and thus allow for access to distant organs. However, the vascular basement membrane in tumors has conspicuous abnormalities (seen here), including multiple layers, and loose association with endothelial cells and pericytes, reminiscent of degenerating or regenerating blood vessels. Magnification: x2500 when printed 10 centimetres wide.