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HOME | Familial Adenomatous Polyposis
Familial Adenomatous Polyposis Syndrome
What is FAP?
Familial Adenomatous Polyposis (FAP) is a precancerous hereditary disease of the gastrointestinal tract. The term “polyposis” refers to a condition of often more than 100 mushroom-shaped growths called polyps on the surface lining of the large intestine. The large intestine, about 1.5 metres long, is divided into the colon and the rectum.
The type of polyp is important because of its potential to become cancerous (malignant). Adenomas, which are the precancerous type, do not develop at birth but may begin to appear in the rectum and colon from puberty onwards. In the beginning, there are frequently no warning signs to alert the patient to the development of polyps.
Adenomas may not be diagnosed for ten years or longer. If left undiagnosed or untreated, one or more of the adenomas may become malignant by age 35-40 years. These figures are meant to represent guidelines rather than specific time limits since some individuals may be affected even after age 45 years. Preventive surgery is required to preclude bowel cancer. Early diagnosis, treatment, and follow-up are essential to cancer control.
Epidemiological studies showed that FAP has a comparable population incidence world wide ranging from 1 : 10,000 to 1 : 20,000. Therefore, it is estimated that about 300 to 600 individuals are affected in Hong Kong.
Who is at risk?
Each child of a parent with FAP has a 50 per cent chance of inheriting the polyposis gene. Genes are the units of heredity in our body cells which pass on traits like eye colour, facial characteristics, and sometimes, diseases. If an affected parent has four children, this does not mean that two will have FAP and two will be unaffected. The chances are the same in each pregnancy that the polyposis gene will or will not be passed on by the affected parent.
If a patient is the first person in the family to be diagnosed with FAP, the patient’s parents, brothers, and sisters should be examined to determine their risk of developing the disease. In about 30 per cent of the patients, a genetic accident occurs in the cell of an unaffected parent and is passed on to the child. This is called a new mutation and it means that there is no family history of the disease.
Immediate family members to be screened are the patient’s adolescent children, brothers and sisters and parents. FAP affects males and females of every race and ethnic group. In general, if a first-degree relative does not inherit the polyposis gene, then his own children will not develop the disease. FAP does not skip generations. One way of understanding who is and who is not at risk for FAP is by starting a family tree and keeping it up to date, with the help of a family study centre or registry (Fig. 2).
How will I know if I have FAP?
Some patients may experience any of the following symptoms : blood in the stool, diarrhoea, crampy abdominal pain, mucous discharge, or weight loss. However, other patients may have absolutely no symptoms indicating adenomas, or possibly cancer, in the large intestine. A child, brother, or sister of an affected patient is still at risk for this disease and should not wait for symptoms to develop. If there is family history of FAP, all at-risk relatives must have a colorectal examination. The different types of examinations are explained below.
Flexible sigmoidoscopy - The introduction of a flexible instrument through the anus for investigation of the colon to about 60 cm (Fig.3). The instrument has a light source, a magnifying eyepiece, and an open channel through which air may be passed, expanding the colon for easier viewing and biopsy, if indicated. Patients with FAP generally have adenomas in the rectum, therefore, sigmoidoscopy is encouraged from the age of 12 to 14 years for each at-risk child, brother, and sister. Maintaining this screening program should be an ongoing and valued family tradition for preventive health care.
Colonoscopy - The passage of a long flexible device from the anus to the junction of the small and large intestine (Fig. 4). This procedure allows detailed exploration of problem areas in the large intestine. Polyps may be biopsied or removed through this instrument. Patients receive light sedation and are usually examined in the hospital as daypatients. Clear liquid is required on the day of the test, along with a laxative and an enema, depending on individual circumstances. A person diagnosed to have FAP by screening sigmoidoscopy requires a colonoscopic examination to determine polyp distribution and the choice of preventive surgery.
Barium enema - The injection of a chalk-like substance (barium) and air through the rectum and into the colon. This radiological test may show lesions in the lining of the large intestine. However, very small polyps may be missed on X-ray. Barium enema does not replace sigmoidoscopy or colonoscopy in early detection of FAP but it may be a supplementary procedure. Bowel preparation may include dietary restrictions, such as liquids only, and a laxative or an enema.
Upper endoscopy - The visual inspection of the esophagus, stomach and duodenum with a long flexible tube which also has a light and lens system. Observation of the inside of the upper gastrointestinal tract permits biopsy or removal of any polyp seen. No food or drink is permitted after midnight prior to the test.
Genetic study - Until 1991, neither scientists nor doctors could predict who would be diagnosed with FAP until polyps occurred. Researchers have now discovered that FAP is a result of mutations in a gene called Adenomatous Polyposis Coli (APC) which is located on chromosome 5. Genetic testing by simple blood taking is now possible to detect such mutations. By genetic testing, we can distinguish with certainly an at-risk family member who is having the abnormal gene (100 per cent chance of having FAP) from another at-risk family member who carries the normal gene (0 per cent chance of having FAP). Relatives having the diseased gene are then advised to undergo endoscopic surveillance at regular intervals and have treatment once polyps develop.
Are there other growths associated with FAP?
There is a wide variation in the number, nature, and development of growths outside the colon which are described as extracolonic growths. The presence of related lesions does not alter the fact that all patients with FAP have colorectal adenomas which require treatment.
Upper gastrointestinal polyps sometimes develop in some patients, particularly in the stomach and duodenum. In the stomach, most polyps identified are not adenomas but multiple tiny cystic-type growths which are benign and do not undergo cancerous change. Adenomas in the duodenum may not be identified on regular X-ray due to their initially small size. Duodenal adenomas may become cancerous if they grow larger and are not checked with biopsy or removal. Often symptomless, these lesions may appear early or a number of years after the diagnosis and treatment of colonic adenomas.
Benign body lesions called osteomas may be present on the skull, face or jaw and can be detected by X-ray. Another external feature is epidermoid cyst, a benign skin lesion. Although common in adults with and without FAP, epidermoid cysts are rare in children and can serve as a warning sign.
Some patients may be born with small freckles at the back of their eyes (retina). These eye lesions are benign and do not change or interfere with eyesight. They appear to be present in some affected families and are formed many years before the colonic adenomas.
There may be a tendency for excess tissue growth in some cases where abnormal lumps of tissue form. These lumps may occur within the abdomen, the abdominal wall, or outside the abdominal area. Known as desmoids, these are benign lesions which may develop after bowel surgery, or less commonly, before FAP has been diagnosed.
Again, extracolonic growths vary from patient to patient, even within members of the same family, and in other cases, may not develop at all.
What is the treatment for FAP?
There is no known medical cure for this disease. Due to the large number of adenomas in the colon, surgery is required to prevent colon cancer. Early diagnosis means early treatment and an improved outcome for the patient. There are several types of surgery available for FAP, depending on the patient and the stage of disease in the colon. In each of the following operations, the patient’s individual needs and circumstances are considered.
Colectomy and ileorectal anastomosis - The removal of the colon, leaving 10 - 15 cm of rectum. The last part of the small intestine (ileum) is joined, or anastomosed, to the rectum. Since part of the rectum remains, the patient must be sigmoidoscoped lifelong at regular intervals to ensure that no new adenomas develop. If the remaining rectum contains only a few polyps, these can be removed or destroyed through the sigmoidoscope. This operation is not suggested if a patient already has cancer, if there are too many rectal adenomas, or if the patient will not return for ongoing examination after surgery.
Restorative proctocolectomy (pelvic pouch) - The excision of the colon, upper part of the rectum, and lining of the lower part of the rectum, leaving the sphincter muscles controlling the urge for a bowel movement. A new rectum, or pouch, is created from the ileum, brought down into the pelvis, and then joined to the anus. Time is needed for the area to properly heal and ensure good function of the pouch. Therefore, a temporary opening (stoma) is made from the ileum to the outside of the abdomen. This surgically created opening is called an ileostomy which means that an external appliance is worn to collect waste products. After about three months, a second shorter operation is required to close the ileostomy. Patients must continue medical follow-up of their pouch as part of their preventive health care. This technical procedure is not recommended for all patients with FAP and should be performed by experienced surgeons. A pelvic pouch should not be done in patients who already have, or subsequently develop, a rectal cancer.
Proctocolectomy - The removal of the entire colon and rectum. A permanent ileostomy is formed and a stoma is created, usually to the right and below the navel so that waste products can pass into an external appliance. This operation may be suggested if there are too many adenomas to control the rectum by other methods or if there is rectal cancer.
Where can I go for more information about FAP?
The Hereditary Gastrointestinal Cancer Registry based at Queen Mary Hospital aims at assisting patients and their families in Hong Kong in learning more about hereditary colorectal tumors, including FAP. By developing a family history, each child, brother, and sister of someone with FAP can understand their need for genetic and colon examination to prevent bowel cancer. We welcome help from family members in keeping the family tree up to date when someone moves, marries, or has a child. For the at-risk family members, we can arrange genetic and endoscopic screening and we can also provide genetic counselling to family members based on the result of family tree and genetic testing. For newly diagnosed patients with FAP, we can arrange surgical treatment, either at Queen Mary Hospital or other specialist centres. Our registry is committed to cancer prevention through early detection, treatment, education, and ongoing research. You can help make cancer control a reality not only for today but for all your tomorrows.
If we can be of assistance, please feel free to write or call us.
家族性結直腸瘜肉綜合症
甚麼是家族性結直腸瘜肉綜合症？
家族性結直腸瘜肉綜合症(FAP)是胃腸道的遺傳性癌前病症。「瘜肉症」這個名詞是指大腸長滿多過一百粒的菇狀瘜肉。1.5米長的大腸分為結腸和直腸。
這種瘜肉病的重要性在於它有轉化為癌症的可能。腺瘤(或稱腺性瘜肉)屬癌前病害,它不會在出世時便生長,卻可於青春期開始在結直腸出現。瘜肉的生長初期很多時是沒有徵狀的,在形成後十年或更長的時間可能也未被診斷。若不加以治理或被發現,在35-40歲時其中一個或幾個腺瘤可能變為惡性(即大腸癌)。請注意,這些祇是參考的數字,而非特定的年歲範圍,因為有些人在45歲以後才病發。瘜肉病患者有必要作預防性的手術以杜絕患大腸癌的機會。控制癌症必須及早診斷,治療及跟進。
根據研究顯示,全世界患家族性結直腸瘜肉綜合症的人口比率為1:10,000至1:20,000。因此推算在香港受影響的人士約為300至600人。
誰有風險？
如父母其中一個患家族性結直腸瘜肉綜合症,每個子女都有五成機會遺傳了瘜肉症的基因(又稱APC基因)。基因就是身體細胞的遺傳單位,把特徵如眼睛的顏色、面部特徵或某些疾病遺傳下去。若父母其中一方受影響,這不代表四個子女其中一半必定受影響。在每個懷孕過程中,受影響的父母都有同樣機會將瘜肉症基因遺傳給子女。
如患者是第一個驗出患有家族性結直腸瘜肉綜合症的話,其父母、兄弟、姊妹應接受檢查以確定他們患病的機會。約三成的患者是由於胚胎基因突變所致。這種過程稱為新基因突變,意指家族沒有發病的歷史。
病人直屬親人需接受普查的包括未成年的子女,病人的兄弟姊妹及父母。不論種族、性別,都會受到家族性結直腸瘜肉綜合症的影響。一般而言,直系親屬沒有遺傳瘜肉症基因,其子女是不會發病的,也不會隔代遺傳。一個方法可以了解誰受家族性結直腸瘜肉綜合症的影響,便是由家庭研究中心或資料庫協助下開記錄及更新族譜。(見註2)
怎樣得悉是否患有家族性結直腸瘜肉綜合症？
有些病人可能有以下經驗:大便帶血、腹瀉、腹部絞痛、排泄黏狀物或體重下降。可是一些病人郤是沒有任何徵狀的。病者的父母、兄弟姊妹及子女均有可能患病,故不應等待病徵出現。若家族有患病紀錄,所有有機會患病的親屬必須進行結直腸檢查。不同種類檢查方式解釋如下:
乙狀結腸及直腸內窺鏡 — 把一條約60厘米長可伸縮的儀器從肛門放入的結直腸檢查。(見圖3)儀器有光源、放大鏡及可供空氣通過的管道,以擴大腸道方便檢查和有需要時抽取活組織。患家族性結直腸瘜肉綜合症的病人一般在直腸內長了腺瘤,每個受響的子女,或其兄弟姊妹,年齡屆乎12至14歲,均鼓勵接受乙狀結腸及直腸內窺鏡檢查。持續定期進行普查,是確保健康的傳統方法。
結直腸內窺鏡 — 把一支1.5米長的內窺鏡由肛門伸展至大腸和小腸的交界。(見圖4)這個過程可以仔細檢查大腸內有問題的部份,也可利用儀器將瘜肉切除或取活組織。有需要會替病人注射輕量的鎮靜劑;檢查通常以日間留院形式進行。視乎個人情況而定,病人在檢查當天會進食流質,輕瀉藥和灌腸劑。以乙狀結腸及直腸內窺鏡進行普查而證實患有家族性結直腸瘜肉綜合症的病人,需要再作結腸內窺鏡檢查,以確定瘜肉的分佈位置和選擇那一種預防性手術。
鋇灌腸X光造影術 — 從直腸將石灰粉狀的物體(鋇)及空氣注入大腸。這個放射性測試可顯示大腸膜的損傷,但X光卻可能錯過細小瘜肉。要早期檢查出家族性結直腸瘜肉綜合症,鋇灌腸X光造影術未能代替內窺鏡檢查,但可作輔助用途。清理腸道的準備包括限制飲食(如祇進食流質)和服用瀉藥或灌腸劑。
腸胃內窺鏡 — 利用內窺鏡檢查食道、胃及十二指腸。除觀察外,更可將胃腸道的瘜肉切除或取活組織。檢查前夕不許飲食。
基因研究 - 1991以前,若未長出瘜肉,科學家和醫生都不能診斷出家族性結直腸瘜肉綜合症。現今研究人員已發現綜合症是由於在第五條染色體的APC基因突變所致。這種突變現時已經可以透過驗血測試出來。以基因測試可分辨出有風險的家庭裡那一位成員帶有突變的APC基因(百份百機會患綜合症)而那一位是帶有正常的APC基因(患綜合症機會是零)。患有綜合症親屬將定期接受內窺鏡監察,若發現瘜肉即加以治療。
與家族性結直腸瘜肉綜合症有關的其他增生？
除大腸瘜肉外,綜合症患者會在身體其他地方有增生,稱為「結腸外增生」。這些相關的增生並不會改變病人要接受結直腸腺瘤治療的事實。有些病人在胃腸道有瘜肉,特別是在胃和十二指腸。在胃發現的瘜肉並非腺瘤,是不會轉為惡性的良性囊狀增生。在十二指腸的腺瘤由於早期體積細小X光未能察覺。但當腺瘤長大後,如未能及時加以切除,便有可能變為惡性。在診斷和治理結腸腺瘤後的初期或數年後,這些增生可能出現,但卻很多時是無徵狀的。
骨瘤是一良性的結腸外增生,它可能是生在頭骨、面部或顎部,X光可檢查出來。另一種良性的增生為表皮囊瘤(或稱粉瘤)。粉瘤常見於成人(非綜合症患者),但綜合症患者會在孩童期間長出粉瘤,因此,可能成為綜合症的警告訊號。
有些病人可能天生眼底(視網膜)長出了斑點。這種良性的眼部增生是不會影響視線的。這些斑點在結腸腺瘤形成之前已在一些受影響家庭的成員發現到。
部份患者可能在腹部、腹壁或身體其他地方長出硬塊,稱為「硬纖維瘤」。硬纖維瘤為良性,大多在腸部手術後出現,但間中也可在綜合症病發前出現。
結腸外增生的種類每個病人都不同,即使在同一個家庭也不一樣,沒有增生的個案也是有的。
怎樣治療家族性結直腸瘜肉綜合症？
現時仍未有根治這種病的方法。由於大腸出現大量腺瘤,因此需要進行外科手術預防結直腸癌。及早診斷可早日治療,效果也較理想。按瘜肉分佈及數目,有幾種手術可供選擇。以下的手術會考慮到病人的情況及需要。
結腸切除及迴腸直腸吻合術-把結腸切除留下10-15厘米直腸。然後將小腸的尾段(即迴腸)接上直腸。手術後,由於仍然剩下部份直腸,病人必須終生接受直腸內窺鏡檢查確保沒有新的腺瘤生長。如剩下的直腸長了少數瘜肉,可在內窺鏡檢查時切除。若病人已患直腸癌症、過多直腸瘜肉、或病人在手術後不會持續接受檢查,則不建議使用這個手術。
恢復性直結腸切除術(骨盆囊袋)-將結腸及直腸切除,留下肛門及括約肌控制排便。用迴腸造成囊袋以代替直腸,將囊袋帶到骨盆然後接上肛門。由於傷口(接合處)需要一段時間復原和確保囊袋運作良好,因此有需要在迴腸處暫造一個造口通出腹外以排泄糞便(即迴腸造口手術)。三個月後,會進行第二個簡短的手術閉合迴腸造口。為著骨盆囊袋的保健起見,病人手術後必須定期覆診。不是所有的綜合症病人也適合接受這種手術,而且是項手術必須由有經驗的外科醫生進行。已患直腸癌或後來患有直腸癌的病人不建議接受骨盆囊袋手術。
結直腸切除術-把整條結直腸切除,並且開一口永久性的迴腸造口。造口的位置一般在肚臍的右下方,用以排泄體內糞便。若病人已患上直腸癌,或者直腸上長滿了腺癌並用其他方法控制不了時,就應該做這種手術。
何處取得更多有關家族性結直腸瘜肉綜合症的資料？
瑪麗醫院的遺傳性腸胃癌資料庫旨在協助病人及其在港家人,學到更多有關遺傳性結直腸腫瘤包括家族性結直腸瘜肉合症的知識。制訂家族譜紀錄可使每個子女,兄弟姊妹患有綜合症的,都能了解以基因和結腸檢查來預防腸癌的重要性。我們歡迎家中成員保持和更新家族譜,記錄任何成員的搬遷、結婚或新生的降臨。有風險的家庭成員我們會安排基因和內窺鏡普查。同時根據基因測試的結果提供輔導。剛驗出患有綜合症的病人,我們會安排在瑪麗醫院或他專科中心進行手術。資料庫是透過及早診斷、治療、教育及不斷研究,致力預防癌病。為未來著想,你也可令控制癌症夢想成真。
如需協助,請與我們聯絡
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