incomplete penetrance

Definition of incomplete penetrance
National Cancer Institute

incomplete penetrance

(in-kum-PLEET PEH-neh-trunts)
A term that describes when some people with a disease-causing mutation (change) in a gene develop the disease while others don’t. For example, certain gene mutations cause cancer, but because of incomplete penetrance, not everyone who has the mutation will develop cancer. Currently, there is no way to know which people who have a cancer-causing gene mutation will develop cancer. Also called reduced penetrance.

Source: NCI Dictionary of Cancer Terms