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Familial adenomatous polyposis (FAP) is an inherited condition in which numerous polyps form mainly in the epithelium of the large intestine. While these polyps start out benign, malignant transformation into colon cancer occurs when not treated.
From early adolescence and onwards, patients with this condition develop hundreds to thousands of polyps. These may bleed, leading to blood in the stool. If the blood is not visible, it is still possible for the patient to develop anemia due to gradually developing iron deficiency. If malignancy develops, this may present with weight loss, altered bowel habit, or even metastasis to the liver or elsewhere.
The genetic determinant in familial polyposis may also predispose carriers to other malignancies, e.g. of the duodenum and stomach. Other signs that may point at FAP are pigmented lesions of the retina (“CHRPE – congenital hypertrophy of the retinal pigment epithelium”), jaw cysts, sebaceous cysts, and osteomata (benign bone tumors). The combination of polyposis, osteomas, fibromas and sebaceous cysts is termed Gardner’s syndrome (with or without abnormal scarring).[1]
Making the diagnosis of FAP before the development of colon cancer is important not just for the individual, but also for the sake of other family members who may be affected. Colonoscopy is considered the diagnostic test of choice as it can provide not only a quantification of polyps throughout the colon but also a histologic diagnosis. Barium enema and virtual colonoscopy can suggest the diagnosis of FAP.
Once the diagnosis of FAP is made, close colonoscopic surveillance with polypectomy is required. Prophylactic colectomy is indicated if more than a hundred polyps are present, there are severely dysplastic polyps, or multiple polyps larger than 1 cm are present. When partial colectomy is performed, colonoscopic surveillance of the remaining colon is necessary as the individual still carries significant risk of developing colon cancer.
Ultrasound of the abdomen and blood tests evaluating liver function are often performed to rule out metastasis to the liver.
Genetic testing provides the ultimate diagnosis in 95%; genetic counseling is usually needed in families where FAP has been diagnosed. Testing may also aid in the diagnosis of borderline cases in families that are otherwise known to have the FAP mutation.
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