APC-associated adenomatous polyposis includes three diseases caused by mutations – or genetic changes – in the APC gene, namely familial adenomatous polyposis (FAP), attenuated familial adenomatous polyposis (AFAP), and stomach cancer with proximal polyposis (gastric adenocarcinoma and proximal polyposis of the stomach, GAPPS).
Starting in adolescence, FAP usually leads to the development of hundreds to thousands of polyps (protrusions of mucous membrane) that are located in the gastrointestinal tract, most frequently in the large intestine. These polyps can progress and result in malignant diseases, such as colon cancer. In addition, there is an increased risk that other benign and malignant tumors will develop.
AFAP is a variant of FAP which is characterized by fewer polyps and a later onset of malignant disease.
GAPPS is characterized by a large number of gastric polyps and an increased risk of stomach cancer. It rarely affects the intestine.