Which body tissue is most likely to develop cancer from equal doses of ionizing radiation?

• A. Small bowel
• B. Spinal cord
• C. Bone marrow
• D. Adrenal glands

Answer: (C)

When ionizing radiation damages DNA, tissues with many rapidly dividing cells and abundant stem cells are most at risk for cancer because those cells constantly replicate and can pass on mutations. Bone marrow fits this pattern best because hematopoietic stem cells in the marrow are continually dividing to replenish blood cells. Radiation can induce mutations in these stem cells, and once a malignant clone starts, it can lead to leukemia.

Spinal cord cells are mostly mature, non-dividing neurons, so they’re far less prone to radiation-induced cancer. The adrenal glands have relatively low cell turnover, and although the small bowel mucosa renews quickly, leukemia from bone marrow exposure is more strongly linked to radiation than cancers arising in that tissue. So, the tissue with the highest cancer risk from equal radiation doses is bone marrow.