Part I
We are all aware of the importance of obesity in the etiology of many types of cancer. But weight loss is a different matter. I am speaking of unexplained, unintentional weight loss—in the absence of dieting, Ozempic, increased physical activity, etc. While a patient will usually report how many pounds have been lost, it is also critical to know the time frame over which this has occurred and the denominator weight—I always ask what the patient considers their normal or usual weight. It is useful to consider weight loss as a percentage of usual weight. Generally speaking, what should raise concern is a weight loss of 10% that persists (e.g., over 15 pounds in a person with a usual weight of 150 pounds), though most would be concerned and consider even a 5% weight loss to be significant. Some sources I consulted stated that an unexplained weight loss of 10 pounds was sufficient to justify a call to one’s physician. Studies show that an unexplained weight loss of 5% or more over several months has a medical explanation about 70% of the time—not necessarily cancer, but something that might need to be addressed.
Unintentional weight loss can be a symptom of multiple diseases and syndromes and so is a real challenge to the primary care physician. Certain conditions are particularly prominent in that evaluation, such as hyperthyroidism, diabetes, celiac disease, or GI tract malabsorption. An emotional or psychological/psychiatric problem such as depression needs to be considered as well. But this is a column on cancer. So what does unexplained or unintentional weight loss tell us about the possibility of cancer? The truth is that there are really no clear-cut guidelines on the work-up of unexplained weight loss from a cancer point of view. Certainly, it can be associated with almost any cancer but there are 10 cancer sites with which weight loss is particularly associated—prostate, colorectal, lung, gastroesophageal, pancreatic, non-Hodgkin lymphoma, ovary, myeloma, renal, and biliary tract cancer.
If there are localizing symptoms, such as rectal bleeding or a productive cough or a pain somewhere, in conjunction with the weight loss, the approach to the diagnostic work-up should be guided by that. But what if the weight loss occurs in an otherwise asymptomatic individual? The truth is that the positive predictive value of work-ups in that context (the probability of finding a cancer) varies considerably but seems to center on about 3% for those around 70 years of age. Interestingly, weight loss is associated with both early stage and late stage cancers, though cancers diagnosed through this symptom tend to be later stage.
What tests are mandated in response to weight loss? I will assume that the primary care physician or healthcare provider will first rule out the general medical conditions associated with weight loss. Again, that can vary by the judgment of the practitioner. Certainly, the routine blood tests and the normative cancer screening tests utilized in wellness examinations should be performed—mammography, colonoscopy, prostate-specific antigen (PSA), etc. After that, there is no consensus.
Why does weight loss occur in people with cancer? Several reasons come to mind. Cancer can cause loss of appetite and lead to people eating less, leading to weight loss. Certainly for cancers that involve sites of the body involved in eating, such as the mouth, neck, or other portions of the gastrointestinal tract, cancer can make it more difficult to eat, to digest, or to absorb food. Occasionally tumors can cause obstruction leading to weight loss. Certain cancers can cause mental health changes, such as depression or anxiety, which can also indirectly lead to weight loss. Finally certain tumors may alter the body’s metabolism, altering the uptake of calories and thus causing weight loss.
I do not want to cause a panic in people over weight loss. There may be changes in your weight because of seasonal changes in clothing, how much you fill your pockets, etc. Also you may alter your physical activity seasonally. Please bear that in mind. But if you do have a true unintentional weight loss, do consider discussing it with your healthcare provider.
In next week’s installment of Thoughts on Cancer we will discuss weight loss in the cancer patient.
Alfred I. Neugut, MD, PhD, is a medical oncologist and cancer epidemiologist at Columbia University Irving Medical Center/New York Presbyterian and Mailman School of Public Health in New York. Email: [email protected].
This article is for educational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment, and does not constitute medical or other professional advice. Always seek the advice of your qualified health provider with any questions you may have regarding a medical condition or treatment.
