One 21-year-old twin got stage 4 colon cancer, the other didn’t… their doctor has a terrifying theory why

Brinlee Luster and her twin sister, Mariela, do everything together.
They went to the same college, studied the same subjects, met their husbands on the same day and even got married just two months apart.
But in 2023, Brinlee had to face a devastating diagnosis alone.
The 21-year-old from Utah suddenly began suffering ‘severe abdominal cramping’ and was so fatigued she could hardly complete a hike that usually came as second nature.
Doctors were quick to dismiss her symptoms as anxiety, side effects of her birth control, or irritable bowel syndrome.
In the midst of planning her wedding and finishing college at Utah State University, Brinlee also put the symptoms down to stress.
But when her symptoms worsened a few months later, a colonoscopy revealed stage four colon cancer.
Mariela, however, has remained healthy, though she did undergo a colonoscopy to remove polyps, which can turn into cancer.
Their case highlights the mystery about what’s causing an explosion of colon cancers in young people.
Brinlee Luster was diagnosed with stage four colon cancer at age 21, just before graduating college and getting married. She is pictured here with her twin Mariela

Brinlee is pictured here while undergoing treatment. The cause of her colon cancer is unclear, though her doctors suggest antibiotic use could be behind the growing cases in young people
Diet, alcohol, obesity and sedentary lifestyles have all been blamed, along with the overuse of antibiotics.
Mariela told KSL News: ‘Having [Brinlee] go through something that I couldn’t go through, and I couldn’t experience, was just so hard.’
Brinlee said: ‘I don’t think anything can prepare you for that moment when you’re told you have cancer.’
Brinlee’s oncologist, Dr Mark Lewis of Intermountain Health, said increasing numbers of his patients are under age 45, the time when doctors recommend regular colon cancer screening.
He told KSL News: ‘There really is unfortunately no such thing as too young for colon cancer.’
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While doctors are still unraveling the causes of America’s colon cancer epidemic, Dr Lewis suggested antibiotic use going all the way back to childhood could be a factor.
He said: ‘Antibiotics in childhood and in adulthood can affect the bacteria that line the colon.
‘We’re being very, very careful about prescribing antibiotics to young people because we do know there is at least a slight increased risk for colon cancer decades later.’
Colorectal cancer is the fourth most common cancer in the US and the second-leading cause of cancer deaths.
The American Cancer Society estimates 154,270 Americans will be diagnosed with colon cancer this year, and 52,900 will die.
This includes 19,550 cases and 3,750 deaths in under-50s.
And by 2030, colon cancer is estimated to be the biggest cancer killer in patients under 50.
Antibiotic use has been a growing concern among colorectal oncologists, as evidence suggests the drugs could permanently alter protective bacteria lining the intestinal tract.
Antibiotics, prescribed more than 230million times a year in the US, are meant to kill harmful bacteria.
However, these medications may also attack the gut’s healthy bacteria, which regulate digestion and help the immune system protect against infections.
This leaves the digestive tract vulnerable to inflammation, which can cause cells to mutate and become cancerous.

Rates of colorectal cancer in Americans under 50 have risen over the past two decades. This graph shows the latest year for which data is available

Brinlee, pictured here, underwent 30 rounds of chemotherapy. She has been in remission since December

Brinlee and Mariela, both pictured here, have started a sweatshirt brand to provide easy IV access for people going through chemotherapy
A 2021 study of more than 40,000 people found antibiotic use was more strongly linked to colon cancer in younger patients than older patients.
The experts believe this could be due to a worldwide increase in antibiotic use, as prescriptions have surged 46 percent across the globe since 2000.
However, experts have also suggested lifestyle factors like obesity, diet, and physical inactivity can also lead to cancer-causing inflammation in the gut.
Brinlee underwent 30 rounds of chemotherapy, completing the treatment in December. She is now cancer free.
Mariela also had a colonoscopy after her sister’s diagnosis, where doctors removed several polyps.
While many of these are harmless, some may develop into cancer due to abnormal cell growth and mutations.
Mariela said: ‘I like to think that she really did save my life in a way because I was headed down that route.’
The twins are working to raise awareness and have also created ‘The Port Studio,’ a line of sweatshirts that provide easy IV access for people going through chemotherapy.
Brinlee said: ‘I don’t want to hide that I had cancer. Sharing your story is uncomfortable, but I want to be able to share it so that people can be inspired.
‘There’s always room for hope.’