Most of the genetic material inside a cell is found in a small structure called the nucleus. Pathologists can see the nucleus by adding a stain called H&E to the tissue. Pathologists use the word hyperchromasia to describe a nucleus that looks darker than normal when examined under the microscope.
Another word for hyperchromasia is hyperchromatic.
A nucleus can show hyperchromasia for different reasons. Non-cancerous cells often show hyperchromasia when they are injured. Pathologists sometimes describe these cells as reactive. Some cancers are also made almost entirely of cells showing hyperchromasia. In this situation, the hyperchromasia used to support the diagnosis.