Anemia is a medical condition defined by a lower-than-normal amount of healthy red blood cells or a reduced level of hemoglobin, the protein responsible for carrying oxygen throughout the body. When the body lacks sufficient oxygen-carrying capacity, common symptoms like persistent fatigue, weakness, and shortness of breath can occur. While anemia is frequently caused by simple and highly treatable conditions, such as iron deficiency or heavy menstrual periods, it can also be a manifestation of a more serious underlying disease, specifically cancer.
The Link Between Anemia and Cancer
Anemia is a recognized complication in individuals diagnosed with cancer, with its prevalence increasing as the disease progresses. Studies suggest that between 30% and 90% of cancer patients may experience anemia at some point during their illness. The presence of anemia is often associated with more advanced stages of cancer and is particularly notable in certain tumor types. Cancers of the gastrointestinal tract and gynecological cancers, for instance, frequently have a higher incidence of anemia at diagnosis. When anemia is detected without an obvious cause, it can prompt a search for potential malignancies. However, anemia rarely occurs as the sole symptom of an undiagnosed cancer and is typically accompanied by other signs, such as unexplained weight loss, persistent pain, or changes in bowel habits.
Mechanisms: How Cancer Causes Anemia
The development of anemia in a cancer patient is a complex process often driven by three distinct biological pathways.
Anemia of Chronic Disease (Inflammation)
One of the most common is the anemia of chronic disease or anemia of inflammation, which occurs because the tumor triggers a sustained inflammatory response. Cancer cells and surrounding immune cells release inflammatory signaling molecules called cytokines. These cytokines interfere with the body’s iron metabolism by promoting the production of hepcidin, a hormone that blocks iron release from storage cells and prevents its proper utilization in the bone marrow for red blood cell production.
Chronic Blood Loss
A second significant mechanism involves chronic, low-level internal blood loss that often goes unnoticed. Tumors located in the gastrointestinal tract, such as in the colon or stomach, can cause slow bleeding from the tumor surface into the digestive tract. This continuous loss of blood eventually depletes the body’s iron stores, leading to iron deficiency anemia.
Bone Marrow Interference
The third mechanism involves the direct physical interference with the body’s blood-making factory, the bone marrow. Certain cancers, including blood cancers like leukemia, originate in the bone marrow, where they proliferate and crowd out the healthy stem cells needed to produce red blood cells. Solid tumors that metastasize to the bone marrow can also physically infiltrate the space, suppressing the production of red blood cell precursors.
Understanding Other Causes and Diagnostic Steps
Common Causes of Anemia
The vast majority of anemia cases are not related to cancer and stem from more common, benign origins.
- Nutritional shortfalls, including insufficient intake or absorption of iron, vitamin B12, or folate.
- Chronic conditions that cause inflammation, such as rheumatoid arthritis, or those that impair hormone production, like chronic kidney disease.
- Heavy menstrual bleeding.
- Regular use of certain non-steroidal anti-inflammatory drugs (NSAIDs), which can cause blood loss over time.
Diagnostic Steps
When a doctor investigates a finding of anemia, the initial step is a Complete Blood Count (CBC). This standard blood test measures the hemoglobin level and hematocrit (the percentage of blood volume occupied by red blood cells). The CBC also provides information about the size and shape of the red blood cells, which helps categorize the type of anemia.
If anemia is confirmed, the next phase involves blood tests for specific markers to pinpoint the underlying cause. These include serum ferritin to check iron stores, as well as levels of vitamin B12 and folate. If these initial tests do not reveal a common cause, further investigation may include an endoscopy or colonoscopy to check for hidden gastrointestinal bleeding, or a bone marrow biopsy.