Anemia is defined by a reduction in the number of healthy red blood cells or a decrease in the concentration of hemoglobin, the protein responsible for transporting oxygen throughout the body. When the body lacks sufficient oxygen-carrying capacity, it can lead to symptoms like extreme fatigue, weakness, and shortness of breath. This complication is highly common within the oncology population, affecting approximately 39% of patients at the time of their cancer diagnosis. For those undergoing active treatment, particularly chemotherapy, the prevalence often increases substantially, sometimes reaching 63% or higher. Anemia diminishes a patient’s quality of life and is associated with poorer outcomes, making it a major focus of supportive cancer care.
Cancers Most Likely to Induce Anemia
The cancers most frequently associated with anemia are those that directly interfere with blood production or cause chronic blood loss. Hematological malignancies, which are cancers of the blood and bone marrow, inherently carry the highest risk. Conditions such as leukemia, lymphoma, and multiple myeloma directly impair the bone marrow’s ability to function. The abnormal, rapidly multiplying cells in these cancers physically crowd out the healthy stem cells that produce red blood cells, suppressing normal blood formation.
Cancers of the gastrointestinal (GI) tract are also highly likely to induce anemia, primarily due to slow, chronic blood loss that often goes unnoticed by the patient. Colorectal and stomach cancers, for example, can bleed internally for extended periods as the tumor erodes blood vessel walls. This persistent loss depletes the body’s iron stores, resulting in an iron-deficiency anemia. Colorectal cancer is frequently cited as the most common malignancy found in patients presenting with unexplained iron-deficiency anemia.
Another group of cancers that frequently cause anemia includes renal cell carcinoma (cancer of the kidney). The kidneys produce erythropoietin (EPO), a hormone that signals the bone marrow to manufacture red blood cells. When a tumor damages the kidney tissue, it can impair this crucial hormone production, leading to a diminished red blood cell count. Furthermore, any advanced cancer that has spread widely (metastatic disease) is highly likely to cause anemia. Metastases that reach the bone marrow physically displace the blood-forming cells, regardless of the cancer’s origin.
How Cancer and Treatment Lead to Anemia
The most common underlying reason for low red blood cell counts in cancer patients is the anemia of chronic disease, also known as anemia of inflammation. The presence of a tumor triggers a state of systemic inflammation, causing the release of signaling molecules called cytokines, such as interleukin-6 (IL-6). These inflammatory cytokines interfere with iron metabolism by increasing the production of hepcidin, a protein that blocks iron from being released from storage sites and prevents its absorption in the gut. This process creates a functional iron deficiency, where the body has iron stores but cannot access them to build new hemoglobin.
Cancer treatment itself also contributes significantly to anemia through a process called myelosuppression. Chemotherapy drugs and radiation therapy are designed to kill rapidly dividing cells, which includes the healthy stem cells in the bone marrow responsible for continuous blood cell production. This damage temporarily suppresses the marrow’s function, leading to a reduction in all blood cell lines, including red blood cells. The severity of chemotherapy-induced anemia depends on the specific agents used, their dosage, and the overall treatment schedule.
Beyond systemic inflammation and treatment effects, two direct physical mechanisms contribute to anemia. One involves the chronic blood loss from tumor sites, which is particularly relevant in gastrointestinal and gynecologic cancers. The other is the direct physical invasion of the bone marrow by tumor cells. When cancer cells metastasize to the marrow, they occupy the space needed for healthy erythropoiesis. In some cases, such as certain lymphomas, the cancer can also trigger an autoimmune response that causes the body to mistakenly destroy its own red blood cells, a condition called autoimmune hemolytic anemia.
Strategies for Managing Anemia
Management of cancer-related anemia often involves a multi-pronged approach tailored to the specific cause and severity of the patient’s condition. For individuals experiencing severe, symptomatic anemia, a red blood cell transfusion provides the fastest and most effective relief. Transfusions rapidly replace the missing hemoglobin, immediately improving oxygen-carrying capacity and alleviating symptoms like severe fatigue and shortness of breath. This intervention is typically reserved for patients with very low hemoglobin levels or those who are experiencing life-threatening symptoms.
Another common treatment involves the use of Erythropoiesis-Stimulating Agents (ESAs), which are synthetic versions of the hormone erythropoietin. These agents stimulate the bone marrow to increase the production of red blood cells over time. ESAs are used to reduce the need for frequent blood transfusions for patients whose anemia is related to chemotherapy. However, their use requires careful consideration due to potential safety concerns, and they are often administered alongside iron supplementation.
Nutritional deficiencies can exacerbate anemia, so supplementation is an important supportive strategy. Since chronic inflammation often blocks the use of existing iron stores, intravenous iron is frequently necessary to replenish reserves and make the iron available for new red blood cell production. Additionally, deficiencies in vitamins such as B12 and folate, which are necessary cofactors for blood cell formation, must be corrected with supplements. Ultimately, the most definitive long-term solution for cancer-related anemia is the successful treatment of the underlying malignancy, as tumor reduction can diminish the systemic inflammation that drives the condition.