Patients are usually excited by weight loss—until they realize it’s cancer
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If [patients] experience significant or rapid weight loss while on the medication but also note any of the other symptoms, there is cause for concern and appropriate medical care should be sought.
Tracey Childs, MD, board-certified general and colorectal surgeon
Weight loss can be a result of loss of appetite due to an inflammatory response, increased metabolic demand of the rapidly growing tumor, associated malabsorption due to diarrhea, and more.
Paul Johnson, MD, colorectal surgeon and surgical oncologist
With cancer rates on the rise—and everyday lifestyle choices fueling the epidemic—clinicians are diagnosing new cases with staggering regularity.
One kind of cancer that has increased by 2.4% per year from 2012 to 2021 in people under 50? Colorectal cancer. About 107,320 new cases of colon cancer are expected to be diagnosed in men and women in 2025 alone. []
The signs and symptoms of colorectal cancer vary, but they generally include bowel habit changes (including diarrhea, constipation, or blood in the stool), abdominal pain and cramps, and weight loss without trying.[]
It’s that last symptom—weight loss—that can be tricky, especially when so many people are on GLP-1s or think of weight loss as an entirely positive thing.
One patient, Shaedra Byrd, says she lost a whopping 100 pounds without trying. “People were telling me that I was slimming down," she said in an interview with People. "When your friends are saying, ‘Hey girl, you're looking good,’ you don't really think that it's something health-wise that you need to look into."[]
She thought the weight loss was simply due to being active with her kids. Eventually, however, she received a devastating diagnosis: stage 3 colon cancer. []
According to a study in Molecular and Clinical Oncology, weight loss in colon cancer can also provide a glimpse into the cancer severity. []
Body weight loss “in patients with colon cancer is not just a symptom, but it is also correlated with tumor location, size and depth, and is a prognostic factor for poor outcomes including overall survival and tumor relapse,” the study authors wrote. []
Clinical tips for questionable weight loss
Michael Cecchini, MD, a medical oncologist and co-director of the Colorectal Program in the Center for Gastrointestinal Cancers at Yale Cancer Center and Smilow Cancer Hospital, says that although there’s no universally accepted indicator of “too much weight loss,” clinicians should be on the alert for patients unintentionally losing more than 10% of their body weight.
Tracey Childs, MD, a board-certified general and colorectal surgeon and chief of surgery at Providence Saint John’s Health Center and adjunct associate professor of surgery at Saint John’s Cancer Institute in Santa Monica, CA, adds that this worrisome weight loss would likely occur within 3 to 6 months.
This weight loss occurs in 15% to 40% of non-metastatic patients and happens for multiple reasons, explains Paul Johnson, MD, a colorectal surgeon and surgical oncologist at Methodist Le Bonheur Healthcare.
“It can be a result of loss of appetite due to an inflammatory response, increased metabolic demand of the rapidly growing tumor, associated malabsorption due to diarrhea, and more,” Dr. Johnson tells MDLinx.
Related: In oncology, 30 is the new 60What about patients taking GLP-1s?
"With the popularization of weight loss drugs like GLP-1 agonists and an increased renewal in weight loss management, the involuntary loss of weight can be masked by intentionality. Therefore, in an ideal world, weight loss should never be the catalyst for colon and rectal cancer screening,” Dr. Johnson says.
“If a patient starts a new medication for weight loss, and that weight loss occurs ... it doesn't necessarily need to trigger a huge warning unless there are other symptoms or [the] patient is extremely high risk for other reasons,” Dr. Cecchini adds.
Dr. Childs agrees: “For people taking GLP-1s, it is anticipated that they will have an expected weight loss of 10-20% of their body weight over several months, and certainly 10 pounds within 3-6 months.”
But if the weight loss is combined with other symptoms, there could be an issue at play: “If they experience significant or rapid weight loss while on the medication, but also note any of the other symptoms, there is cause for concern and appropriate medical care should be sought,” Dr. Childs says.
These other symptoms include fatigue, abdominal pain, nausea or vomiting, and persistent change in bowel habits, including changes in texture (such as loose stool), size, or frequency.
Related: Her smart ring knew she had cancer 8 months before docs finally listened