Cancer. Hemoglobin is what binds with the oxygen in the blood stream, carrying it to the rest of your body. Inadequate iron supply is the main cause as to why hemoglobin levels are low. Cancer is the disease where cells continue to grow and divide without stopping. This usually causes the formations of tumors found in a variety of areas in the body. Anemia, the general term for any micro-nutrient deficiency, is one of the main causes of cancer in cancer patients. The protein, hemoglobin is mainly composed of iron. A high blood cell count, specifically white blood cells is very common among cancer patients. This is do to the human body sending antibodies to an infection among the body to fight and kill the infection. When this happens, a significant decrease in the hemoglobin occurs because the body is trying to send the most oxygen to the infectious area. Thus causing a decrease in hemoglobin, as well as a decrease in iron.