PJS causes certain physical features. These can include:

• Dark blue or brown moles around and/or in the mouth (including the lips), and around the eyes, nostrils, and anus. There may be dark moles on the hands and feet. These appear during childhood and fade with age.
• Polyps in the gastrointestinal tract that appear in childhood and cause pain, bleeding, and blockages
• Polyps in other parts of the body, like the nose, lungs, and bladder
• Increased risk of benign (not cancer) tumors of the ovaries and testes

PJS is caused by changes (mutations) in a gene. This gene is called STK11. It is on chromosome 19. Genetic testing can find this gene change. About half of the people diagnosed with PJS have a family history of the disorder. The other half have no family history. Almost all people with PJS will be diagnosed with 1 or more of these types of cancer during their lifetime:

• Ovarian
• Breast
• Colon
• GI tract
• Pancreas
• Cervix
• Testicular

The STK11 gene is a tumor suppressor gene. This gene usually controls cell growth and cell death. Both copies of a tumor suppressor gene must be mutated before a person will develop cancer. With PJS, the first mutation is inherited from either the mother or the father. This gene is present from birth in every cell of the body. This is called a germline mutation. Whether a person who has a germline mutation will develop cancer and where the cancer(s) will grow depends on where the second mutation happens. For example, if the second mutation is in the breast, then breast cancer may grow. If it's in the colon, then colon cancer may grow.

More than 1 growth-control genes need to mutate before a tumor can develop. Loss of STK11 is just the first step in the process. What causes these other mutations is unknown. Possible causes include:

• Contact with certain chemicals
• Contact with certain biological environmental factors
• Errors in cell replication that happen by chance

Some people who have inherited a germline STK11 mutation never have cancer. This is because they never get the second mutation that stops the function of the gene and starts the process of tumor growth. This can make the cancer appear to skip generations in a family. But the gene mutation is still present. People with a mutation have a 50/50 chance to pass the mutation on to each of their children. This is true whether or not they develop cancer.

The STK11 gene is not on the sex chromosomes. This means the mutations come from either the mother's side or the father's side of the family.

Genetic testing can confirm if you have PJS. People with PJS can take steps to reduce cancer risk. For example, these can include not using tobacco and staying away from tobacco smoke. It's also important to talk to a healthcare provider about cancer screening, such as:

• Upper endoscopy. Starting at age 8, a child with PJS should have these tests regularly. These are done to watch for polyps and tumors in the esophagus.
• Colonoscopy. At age 8, a child with PJS should have this test. If polyps are found, the test should be done every 2 to 3 years. This checks for changes that could become cancer over time.
• MRI tests. These can be done to watch for pancreatic cancer. This should be done starting at about age 30.
• Mammograms. These tests should be started at age 20.This should be done every 2 to 3 years until age 40. They should then be done once a year.
• Yearly pelvic exam. These should be done with ultrasound for women with PJS, starting at age 25.
• Yearly testicular exam. These should be done for men with PJS, starting at age 25.

The best screening plan varies for each person. Talk to your provider about seeing a genetics doctor to figure out the best plan for you.