Large red blood cells, called macrocytosis, are not a cancer symptom but may signal a problem that needs to be examined medically, explains Mayo Clinic. Macrocytosis is not a disease and does not produce symptoms or signs. Vitamin B-12 or folate deficiencies, liver disease, hypothyroidism and alcoholism commonly cause macrocytosis.
Drugs that treat seizures, cancer and autoimmune diseases can cause red blood cells to become larger than normal. The condition can develop when bone marrow regenerates red blood cells to compensate for anemia after a loss of blood, notes Mayo Clinic. Doctors typically discover macrocytosis during a routine blood test. If folate or vitamin B-12 deficiency is causing the condition, a patient may need dietary changes or vitamin supplements. A patient suffering from severe anemia may need a blood transfusion.