Pathology dictionary -


A precursor is an abnormal group of cells that have the potential to turn into cancer over time. Another name for a precursor is a pre-cancerous disease. 


Some precursors have a low chance for turning into cancer while others have a very high chance. The chance that a precursor will eventually turn into cancer depends on many factors including:


  • The type and location of the precursor disease.

  • The size of the precursor disease.

  • The grade of the cells in the precursor.


Pathologists look for these changes when examining tissue under the microscope.


Precursor diseases can be caused by viruses, genetic changes, or environmental factors. A common virus that causes a precursor disease is human papillomavirus (HPV). Smoking is a common cause for precursor diseases in the mouth, throat, and lungs.

Doctors often look for precursor diseases so they can be treated before they have a chance to become a cancer. This type of examination is called screening and it is meant to reduce a person's chance of developing cancer in the future. Common types of screening examinations include the cervical pap test and colonoscopy.

Common types of precursor diseases include:

  • High grade squamous intraepithelial lesion (HSIL) - This precursor is caused by a virus called human papillomavirus (HPV). This precursor can cause a cancer called squamous cell carcinoma in the cervix, vulva, vagina, and anal canal.

  • Adenomas of the colon - These small growths are very common in adults over 50 years old. Types of adenomas include tubular, villous, and tubulovillous. They are caused by a combination of environmental conditions (for example diet) and genetic changes in the cells that line the inside of the colon. Adenomas can turn into a type of colon cancer called adenocarcinoma. A procedure called a colonoscopy can be performed to look for and remove adenomas in the colon.

  • Barretts esophagus - This is a precursor disease that happens in the esophagus. It usually develops after many years of acid reflux disease. Barretts esophagus can turn into a type of esophagus cancer called adenocarcinoma. The chance of developing cancer is low for most people but it increases if your pathologist also sees a change called dysplasia.

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