Radiotherapy: A Breast Cancer Solution for Some, but Not All
Written by Daphne Crum
Edited by Emily Moran
Jan 31, 2021
Edited by Emily Moran
Jan 31, 2021
Radiation therapy is the most common form of breast cancer treatment after mastectomies, but about 20% of patients who undergo radiotherapy suffer serious side effects (Borrego-Soto, “Ionizing Radiation-Induced DNA Injury and Damage Detection in Patients with Breast Cancer”). Worsening symptoms result from the failure to avoid damaging healthy cells while using radiation to eliminate cancer cells, and unlucky patients whose cells fail to repair their own DNA strand breakages suffer the most. How is a doctor to know a patient’s tolerance for radiation before undergoing treatment?
Radiotherapy is organized into two categories. Internal radiotherapy requires that a radioactive element be surgically implanted at the site of the tumor, releasing gamma radiation to destroy cells. External radiotherapy beams x-rays at the tumor using an electronic linear accelerator. Some patients are administered multiple rounds of radiation per day while others are treated with larger doses of radiation administered less frequently. Reducing treatment time can combat and control rapidly-growing tumors more effectively, but lowering the radiation dosage lessens the intensity of side-effects.
The ionizing radiation used to penetrate our bodies should only induce DNA breaks in cancer cells, but there is no guarantee that healthy cells in surrounding tissues can be spared. Double-stranded breaks in healthy cells can result directly from the radiation or from reactive oxygen species generated as a result of radiation exposure. If healthy cells cannot repair themselves, permanent chromosomal damage results in toxicity that leads to nausea and severe skin reactions, and even new cancer growths can develop (“Side Effects of Radiation Therapy - Canadian Cancer Society”). Patients who experience the worst symptoms are considered highly radiosensitive.
Doctors Gissela Borrego-Soto, Rocío Ortiz-López, and Augusto Rojas-Martínez have conducted research to understand the genes involved in DNA repair. Their studies focus on the implications of identifying cellular responses to radiation using various diagnostic techniques.
One test analyzed samples of white blood cells in breast cancer patients following radiation exposure. Mutations occurred in 153 genes and the signatures of 67 of those genes arose most prominently in radiosensitive patients. Only the mutations in two genes, XRCC3 and RAD51, were specifically linked to radiosensitivity. Scientists will need to apply radiation to other tissue types to identify more gene breaks that indicate a direct correlation to severe reactions.
Another test analyzed the presence of an 8-oxo-dG biomarker in the urine of breast cancer patients following radiation exposure. Biomarkers are substances released by tumors and from the body responding to a tumor (“Biomarkers to Guide Treatment for Metastatic Breast Cancer”). A higher concentration of 8-oxo-dG was found in radiosensitive breast cancer patients, possibly indicating a higher level of radiation-induced oxidative stress. This stress occurs when radiation breaches cells and frees electrons that then latch onto oxygens, forming dangerous oxygen species that damage DNA nucleotides (“Oxidative DNA damage: Mechanisms, mutation, and disease”). High 8-oxo-dG levels could suggest the formation of oxygen species as a result of radiation, but the same biomarker also appears when cells are exposed to pollution from the environment, so this test wouldn’t be perfectly accurate.
With more conclusive research, performing these tests before clinical decisions are made could eventually help doctors identify which patients are strong candidates for radiotherapy and which are not, revolutionizing individualized breast cancer treatment.
Works Cited
“Biomarkers to Guide Treatment for Metastatic Breast Cancer.” Cancer.Net, 20 July 2015,
www.cancer.net/research-and-advocacy/asco-care-and-treatment-recommendations-patients/biomarkers-guide-treatment-metastatic-breast-cancer. Accessed 30 Oct. 2020.
Borrego-Soto, Gissela, et al. “Ionizing Radiation-Induced DNA Injury and Damage Detection
in Patients with Breast Cancer.” Genetics and Molecular Biology, Sociedade Brasileira
De Genética, Dec. 2015, www.ncbi.nlm.nih.gov/pmc/articles/PMC4763322/. Accessed
20 Oct. 2020.
Cooke, M., Evans, M., Dizdaroglu, M., Lunec, J. (2003, July 01). “Oxidative DNA damage:
Mechanisms, mutation, and disease.” FASEB, 3 July 2003,
https://faseb.onlinelibrary.wiley.com/doi/full/10.1096/fj.02-0752rev. Accessed 8 Nov.
2020.
Schraer, Rachel. “Breast Cancer: One-Dose Radiotherapy 'as Effective as Full Course'.” 19 Aug.
2020, www.bbc.com/news/health-53834130?xtor=AL-72-%5Bpartner%5D-%5Bbbc.
news.twitter%5D-%5Bheadline%5D-%5Bnews%5D-%5Bbizdev%5D-%5Bisapi%5D. Accessed 11 Nov. 2020.
“Side Effects of Radiation Therapy - Canadian Cancer Society.” Canadian Cancer Society, 2021, www.cancer.ca/en/cancer-information/diagnosis-and-treatment/radiation-therapy/side-effects-of-radiation-therapy/?region=on. Accessed 26 October 2020.