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Kirstie Alley died of colon cancer. These are the disease's early signs.

Colorectal cancer is the fourth-most common cancer in the U.S. Doctors recommend a colonoscopy every 10 years for people ages 45 and up.

Following the news that actor Kirstie Alley died of colon cancer at age 71, several doctors and cancer specialists urged people to get the recommended screenings for the disease.

Alley's manager confirmed to NBC News on Tuesday that the actor died of colon cancer. Alley’s family said in a statement on Monday night that the cancer had only recently been discovered.

"She was surrounded by her closest family and fought with great strength, leaving us with a certainty of her never-ending joy of living and whatever adventures lie ahead," the statement said.

Colorectal cancer is the fourth-most common form of cancer in the U.S. and the second-most deadly behind lung cancer. The National Cancer Institute estimates that around 151,000 cases of colorectal cancer will be diagnosed this year.

Colon cancer can be difficult to diagnose, however, since symptoms can resemble those of other conditions like hemorrhoids or irritable bowel syndrome.

"Unfortunately, colon cancer doesn't have a lot of symptoms until it's advanced, which is why screening is so important," said Dr. Paula Denoya, director of the Colorectal Surgery Residency Program at Stony Brook Medicine.

The pandemic also most likely delayed detection of some new cases, according to Dr. Scott Kopetz, a professor in the department of gastrointestinal medical oncology at the University of Texas MD Anderson Cancer Center.

"Patients have not had access to routine colonoscopy readily during Covid. As a result, cancers that would have been caught at an earlier stage are now presenting with more advanced and later stage," he said.

Nearly 90% of colorectal cancer patients are age 50 or older, so doctors recommend that everyone over 45 get a colonoscopy every 10 years.

But diagnoses in younger adults have been rising: New cases of colorectal cancer went up more than 2% each year among people under 50 from 2012 to 2016, according to the American Cancer Society.

"There’s an expectation there will be 15% of colorectal cancers in people under 50 not too long from now," said Dr. Joel Levine, co-director of the Colon Cancer Prevention Program at UConn Health.

Overall, the rate of new colorectal cancer cases in the U.S. has declined, from around 67 per 100,000 people in 1985 to around 34 in 2019, according to the National Cancer Institute.

Early signs of the disease can include rectal bleeding or changes in bowel movements such as constipation or diarrhea. Patients with more advanced illness may also experience abdominal pain, fatigue, anemia, weight loss or decreased appetite.

But Levine said people should get colonoscopies even when they feel healthy.

"One of the reasons I’m so fussy about not waiting for symptoms is because it leads to, 'Well, I feel alright, everything’s OK.' And by the time you have a symptom, the horse is a little bit out of the barn," he said.

Colonoscopies allow doctors to examine the colon and remove precancerous growths, which can prevent cancer from forming. However, the procedure usually involves sedation or anesthesia and can cost thousands of dollars without insurance.

"Patients have barriers to getting colonoscopies, whether it be insurance, whether it be time off work, they don’t want to do it or they have medical problems that make it higher risk," Denoya said.

As an alternative for patients facing these issues, doctors sometimes suggest a stool test. There are various types: One, called Cologuard, can detect changes in a person’s DNA and should be done every three years. Denoya said that test is good at finding cancer but less effective at flagging precancerous growths.

A second type of stool test, called the FIT, looks for hidden traces of blood that may signal the presence of cancer. Denoya said that test should be performed annually. If either test returns abnormal results, doctors will still recommend a colonoscopy.

Beyond age, other risk factors for colon cancer include obesity and lifestyle factors like smoking or drinking.

More than half of colorectal cancer diagnoses in the U.S. are attributable to behavioral patterns, including physical inactivity, diets high in red or processed meat, and a low intake of fruits, vegetables and fiber.

A family history of colon cancer can also raise one's risk.

"If somebody has a parent or sibling that had colon cancer, then that person would start screening 10 years younger than [when] their family member had it," Denoya said.

Patients diagnosed early have a high survival rate.

"If the patient is diagnosed with a stage one or localized cancer, where it's just in the colon and hasn't moved elsewhere in the body, it's about 90% curative just with surgery," Denoya said.

More advanced cases may require chemotherapy or radiation. People whose tumors have spread to nearby lymph nodes or areas around the colon have a 72% survival rate after five years. The rate drops to 14% for patients whose cancer has spread to other organs or more distant lymph nodes.