What type of cancer affects blood-forming cells in bone marrow?

Leukemia is a type of cancer that specifically affects the blood-forming cells within the bone marrow. This cancer disrupts the normal production of blood cells, leading to an overproduction of abnormal white blood cells. These leukemic cells can crowd out normal cells, impairing the body's ability to produce healthy blood components, including red blood cells and platelets, which can lead to a variety of health complications.

In contrast, sarcoma primarily affects connective tissues such as bones, cartilage, and fat. Carcinoma is a cancer that originates in the epithelial cells, which line the surfaces of organs and structures throughout the body. Melanoma is a form of skin cancer that develops from melanocytes, the cells responsible for pigment production in the skin. Each of these types of cancer has distinct characteristics and affects different parts of the body, which is why leukemia is the correct answer in this context.