Sometimes people with cancer become anemic as a result of their cancer, treatment, and weak body. I find the processes (there are four, listed below) that cause this anemia to be quite interesting. (Note: anemia is when the body doesn't have enough iron. The main symptom of anemia is fatigue).
1) Cancer cells sequester iron because they need it for their metabolism. But so do normal cells. As a result, the body "hides" iron from the cancer cells in the liver. The body stores it instead of using it. The body also wants to "hide" iron so much that it downregulates new iron synthesis too.
2) Inflammation, due to the war between the immune system and the cancer cells, causes the liver to stop making iron (iron restricted erythropoiesis) and decreases the synthesis of erythropoietin (EPO). EPO normally stimulates red blood cell (RBC) production, meaning more iron is made (every RBC contains one iron molecule). The inflammation also causes the bone to stop responding to EPO, meaning fewer RBCs and thus less iron.
3) Nutritional deficiencies contribute to the low iron levels (cancer patients have poor appetites and thus aren't typically eating iron rich foods).
4) Chemotherapy (chemo) treatment also makes the bone marrow not respond to EPO (as did the inflammation above). Chemo treatment also decreases appetite and evokes vomiting, adding to the nutritional deficiencies (described above). Surgery in conjunction with chemo may result in some blood loss, causing blood/RBC loss and yet again iron.
I find these connections to be fascinating, but maybe that's because I am a science junkie :P If this blog post was too technical don't worry, because I'll be back tomorrow with a nice and sweet (literally) post about chocolate :)