Dr. Pan's Blog

 

Hereditary colorectal cancer
Nov 2010

In this issue of the blog, I have invited Dr. Dan Li, our gastroenterologist, to write about hereditary colorectal cancer. The majority of colorectal cancers are unrelated to family history, and is called sporadic cancers. Treatment and surveillance for patients with hereditary cancer are often different from sporadic cancers.

Dr. Li has taken time to elaborate on each syndrome that is related to an elevated risk of colorectal cancer. Dr. Li is a highly regarded and accomplished physician. Dr. Li graduated from Peking Union Medical College, the only eight-year medical school in China. He completed residency at Harvard Medical School and gastroenterology specialty training at the University of California at San Francisco.
---Dr. Pan

Hereditary colorectal cancer
---by Dr. Dan Li, MD, Department of Gastroenterology

It is estimated that 20% of patients with colorectal cancer have a positive family history.  Among these individuals, some have a very strong family history of colorectal cancer as well as other cancers.

• These patients actually carry certain gene mutations in their DNA and have so-called “hereditary colorectal cancer syndromes”.
• The term “syndrome” is used here because the condition usually involves multiple organ systems in the body.
• The most common hereditary colorectal cancer syndromes include:
• Lynch syndrome (also called hereditary non-polyposis colorectal cancer, HNPCC)
• familial adenomatous polyposis (FAP)
• hamartomatous polyposis syndrome
• hyperplastic polyposis

Lynch syndrome
Lynch syndrome is the most common type of colorectal cancer syndrome. The syndrome is named after Dr. Henry Lynch, the oncologist who pioneered the study of this disease decades ago.

• It is caused by mutations in genes responsible for repairing DNA defects of the cells.
• These genes are called DNA mismatched repair genes. Mutations of two genes called MLH1 and MSH2 are responsible for 90 percent of this hereditary cancer syndrome.
• Other less common gene mutations include MSH6, PMS1, and PMS2.  Recently, defects in another gene called EpCAM (TACSTD1) were also found in some families with Lynch syndrome.

Individuals who carry one of these mutations are at an estimated 80% lifetime risk of developing colorectal cancer.

• They are also at increased risk of cancer of other organs, such as endometrium, ovary, stomach, ureter, renal pelvis, skin and others.

Women with Lynch syndrome have 40-60% lifetime risk of developing endometrial cancer, and 5-12% lifetime risk of developing ovarian cancer.

Current guidelines recommend screening colonoscopy in affected individuals be initiated by age 20-25 years of age, and repeated every 1-2 years.

• Once cancer develops, subtotal colectomy with ileorectal anastomosis should be considered.
• Annual rectal surveillance is indicated thereafter. 
• Prophylactic colectomy is also an option for men and women diagnosed with Lynch syndrome even prior to the appearance of cancer. .
• For women, prophylactic hysterectomy and bilateral salpingo-oophorectomy (resection of the ovaries) should be discussed as an option after completion of childbearing.   

 
For more information, this link takes you to NIH genetics website on Lynch syndrome.

Familial adenomatous polyposis (FAP)
The second-most common inherited colorectal cancer is called familial adenomatous polyposis (FAP).

• This disease occurs in about 1 in 10,000 individuals. 
• It is caused by mutations in a gene called APC.
• Individuals with this condition inherited mutations from their parents or developed new mutations in their own genes (so-called de novo mutations).  
• Patients with FAP can develop hundreds to thousands of polyps in their colon starting at a young age. 
• The colon cancer risk in their lifetime is close to 100%. 
• The average risk for colon cancer diagnosis in these individuals, if untreated, is 39 years, but 7% develop colon cancer by age 21 and 95% by age 50.
• There is also a less aggressive form of FAP, called attenuated FAP. 
• Individuals with this latter condition tend to have a less number of polyps (dozens to hundreds). Their lifetime risk for colon cancer is about 70%.

In addition to colon cancer, individuals with FAP and attenuated FAP are also at increased risk of developing cancers throughout the gastrointestinal tract, particularly cancer in the duodenum.

• They can also develop tumor or cancer in other organs such as bone, soft tissue, thyroid, retina, and others. 
• Individuals who are at risk for FAP or who are already diagnosed with FAP should have colonoscopy every 1-2 years, beginning at age 10-12 years until a decision is made to perform surgery to remove the colon given the extremely high risk of colon cancer in their lifetime.

 
For more information about this hereditary condition, visit the NIH genetics page:

 

Below I also discussed about some less common hereditary colorectal cancer syndromes:

MUTYH-associated polyposis (also referred to as MYH-associated polyposis, MAP). 

• Patients with this condition carry gene mutations in the MYH gene.
• These individuals tend to develop multiple precancerous polyps in their colon and have an increased risk of colorectal cancer. 
• In addition, they also have an increased risk of ovarian, bladder, skin, and sebaceous gland tumors, and possibly breast cancer.

Hamartomatous polyposis syndromes:
1) Peutz-Jeghers syndrome

• This syndrome is caused by mutations in STK11 (LKB1) gene.
• Individuals with this condition have multiple hamartomatous polyps in the small intestine (in 96% of patients), stomach (25%) and colon (30%).
• A characteristic finding in patients with Peutz-Jeghers syndrome is the dark colored spots on the lips, buccal mucosa, and around eyes.
• Patients with Peutz-Jeghers syndrome have an estimated 70% lifetime risk of gastrointestinal cancer and 50% lifetime risk of breast cancer, as well as 11-36% risk of pancreatic cancer.
• Genitourinary cancers in females and testicular cancer in males may also occur. 

2) Juvenile polyposis syndrome

• This condition results from mutations in either SMAD4 or BMPR1A gene.
• Individuals with juvenile polyposis develop multiple juvenile polyps in the colon, stomach, duodenum and small bowel, with about 39% lifetime risk of colorectal cancer.
• Cancers in the stomach, small bowel and pancreas may also develop.

3) Cowden syndrome

• This condition is associated with mutations in a gene called PTEN.
• This gene is a tumor suppressor gene that can block tumor from developing.
• When PTEN is mutated, it has lost the ability to suppress tumor and cells that harbor PTEN mutation can grow out of control and become cancerous.
• Cowden syndrome patients develop benign tumors of skin gastrointestinal tract, and nervous system, and at increased risk of developing cancer of breast, thyroid, uterus, and others.
• Cowden is named after Rachel Cowden, the first patient identified with this syndrome.  

4) Hyperplastic polyposis:
Hyperplastic polyposis is a rare condition characterized by multiple hyperplastic polyps in the colon.

• The polyps tend to be large, and tend to reside in the proximal colon.
• The patients with this condition have an increased risk of developing colorectal cancer.
• To date, the cause and natural history of this condition is not known. 
• The World Health Organization’s criteria for hyperplastic polyposis include:
1. at least 30 hyperplastic polyps of any size distributed throughout the colon
2. at least 5 hyperplastic polyps proximal to the sigmoid colon with at least two polyps >10mm in diameter;
3. at least one hyperplastic poly in an individual with a first-degree relative with hyperplastic polyposis.

Individuals with this condition should have screening colonoscopy every 1-2 years.