Radiotherapy promotes cancer invasion and metastasis

The goal of conventional cancer treatment is to remove or shrink the size of the tumor, as doctors believe that once the tumor is reduced or removed patients will be trouble free, even though in reality, such is not the case. 

Radiotherapy based on ionizing radiation and indicated to shrink the cancer mass can actually worsen the condition of the disease, according to a new study reported in the June 2010 issue of PLoS One. 

The study led by Barata J.T. and colleagues from Faculdade de Medicina da Universidade de Lisboa in Lisbon, Portugal found ionizing radiation for cancer treatment promotes tumor invasion and metastasis.  

That probably explains why after cancer treatment, cancer returns or spreads to other organs in many patients. 

The problem with radiotherapy is that ionizing radiation, when delivered during fractionated radiotherapy, boosts cancer spreading and aggression.  This effect was also observed in the area surrounding the tumor. 

Ionizing radiation per se is a well known cancer causing agent at low doses, according to the National Toxicology program. 

The authors of the study said doses of ionizing radiation lower or equal to 0.8 Gy can enhance endothelial cell migration. 

Here’s what happens, specifically: tissue exposed to low doses of ionizing radiation experiences rapid phosphorylation of several endothelial cell proteins such as the Vascular Endothelial growth factor, or VEGF Receptor-2. 

When VEGF Receptor-2 is activated, low doses of ionizing radiation enhances endothelial cell migration and prevents endothelial cell death, which is otherwise promoted by anti-angiogenic drug bevacizumab. 

The authors also used murine experimental models of leukemia and orthotopic breast cancer and demonstrated that low doses of ionizing radiation promotes tumor growth and metastasis. 

The good news is that this adverse effect can be prevented by using a VEGF receptor-tyrosine kinase inhibitor immediately prior to ionizing radiation exposure.

By Jimmy Downs and editing by Rachel Stockton

Source:  

PLoS One. 2010 Jun 21;5(6):e11222.

Low doses of ionizing radiation promote tumor growth and metastasis by enhancing angiogenesis.

Sofia Vala I, Martins LR, Imaizumi N, Nunes RJ, Rino J, Kuonen F, Carvalho LM, Rüegg C, Grillo IM, Barata JT, Mareel M, Santos SC. 

Angiogenesis Unit, Instituto de Medicina Molecular, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal.