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How cancer develops
Cancer begins as a cluster of normal cells (hyperplasia). Over time, the cells can develop abnormalities (atypical hyperplasia) that make them different from normal cells, but not yet cancerous. The abnormal cells may continue to change in appearance and multiply, evolving into noninvasive (in situ) cancer or, eventually, invasive cancer. Invasive cancer can spread to other areas of the body through the bloodstream or the lymphatic system.