Cancer rarely stays in the same place, which makes fighting it extremely tricky. Tumour cells can spread to other parts of the body via the lymph system - a complicated network of vessels and nodes. The patient pictured has head and neck cancer (largest yellow blob near mouth is a tumour). The smaller blobs are sentinel lymph nodes – the first nodes any cells from the tumour are likely to reach. The sentinel nodes have been identified using SPECT imaging, which works by tracking a radioactive substance through the lymph system. The tracer is injected near the tumour, and emits gamma rays, which are detected by a special camera. When the tracer drains into lymph nodes the bright hotspots result. These nodes must now be removed by a surgeon and tested for tumour cells, so doctors know what stage the cancer is at, and where to target treatment.
Written by Emma Stoye
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