Persistent Fatigue: When It's a Warning Sign

This page is for anyone who feels tired all the time and wonders if cancer could be the cause. It explains how cancer-related fatigue differs from ordinary tiredness, the common causes, and what a doctor may check.

Everyone feels tired sometimes. Ordinary tiredness gets better with sleep or a day off. Cancer-related fatigue is different. It does not fully improve with rest, and it can get in the way of daily life. It can be an early sign of some cancers, especially blood cancers. It has many other causes too, so it should be checked rather than assumed.

Leukemia, a cancer of the blood and bone marrow, can cause fatigue early on. Leukemia cells crowd out the bone marrow's ability to make healthy red blood cells, which carry oxygen through your body. Fewer healthy red cells means less oxygen reaching your tissues, which shows up as tiredness. Some other cancers cause blood loss. That can lead to anemia, a low red blood cell count, and fatigue. Fatigue is one of the listed signs of colon cancer, along with blood in the stool.

It is often described as a heavy, whole-body tiredness that sleep does not fix. Simple tasks, like climbing stairs or making dinner, can feel harder than they should. Some people also notice shortness of breath, a fast heartbeat, chest pain, dizziness, or looking pale. These are all signs that can go along with anemia.

Many other things cause fatigue:

• Poor sleep.
• Stress, depression, and anxiety.
• Thyroid problems.
• Infections.
• Some medicines.
• Anemia from low iron or other causes. Most people with anemia do not have cancer.

Your doctor asks how long the fatigue has lasted, whether rest helps, and whether you have noticed other symptoms like weight loss, fever, or bleeding. A complete blood count is one of the first and most useful tests, since it checks your red blood cells, white blood cells, and platelets in one simple blood draw. If it shows anemia, further tests look for the cause. Thyroid, kidney and liver tests and a urine test are common too.

A normal complete blood count is reassuring. But it does not rule out every cancer, especially ones that have not yet affected your blood counts. If fatigue continues for several weeks with no cause found, tell your doctor rather than letting it go. Fatigue that does not improve after treating an identified cause, like a thyroid problem, also deserves a second look.

Write down how long you have felt this way. Note whether rest helps at all. Track any other changes, like appetite, weight, or bruising. Bring a list of your medicines too. This short record helps your doctor separate ordinary tiredness from a pattern that needs testing.

• Call 911 or go to an emergency department if you are short of breath even at rest, have chest pain or an irregular heartbeat, black out, have new or worse confusion, or have bleeding that won't stop. Do not drive yourself.
• Call your care team right away if the tiredness comes with dizziness, blurred vision, or little or no urine. If you have thoughts of harming yourself, call 911.
• Call your care team the same day if the tiredness comes with bruises you cannot account for, bleeding gums, or a temperature of 100.4°F (38°C) or higher.
• Call your care team within a day or two if you have felt wiped out for several weeks and rest changes nothing, or weight is coming off on its own alongside it.

• Could my fatigue be caused by anemia or another condition?
• What tests would help find the cause?
• Should I have my blood counts checked?
• What changes should prompt me to come back sooner?

• American Cancer Society — Is Anemia a Sign of Cancer?
• American Cancer Society — Signs and Symptoms of Cancer
• MedlinePlus — Fatigue
• National Cancer Institute — Colon Cancer Treatment (PDQ)
• National Cancer Institute — Adult Acute Lymphoblastic Leukemia Treatment (PDQ)