This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hematopoeisis: Basic concepts, Subject name: Pathology
A 56-year-old woman with a history of breast cancer that was treated 5 years ago with lumpectomy and radiation but with no chemotherapy returns with bone pain, fatigue, and weakness. A complete blood count reveals severe anemia, as well as decreased white blood cells and platelets. Examination of a peripheral blood smear reveals small numbers of nucleated red cells, as well as an occasional "blast" cell and myelocyte. A likely cause of the hematologic abnormalities is 
Select and explain. 
A. chloramphenicol., B. Diphyllobothrium latum infestation., C. megaloblastic anemia., D. myelophthisic anemia.
D: myelophthisic anemia.
Answer: D: myelophthisic anemia. 
Explanation: - Infiltration of tumor cells from cancers, those of breast & prostate - displaces bone marrow elements, thereby causing myelophthisic anemia. OTHER OPTIONS: - Chloramphenicol causes aplastic anemia in some individuals. - Diphyllobothrium latum infestation can result in megaloblastic anemia due to vitamin B12 deficiency.