Radiation therapy after breast cancer surgery does not raise skin cancer risk, Seoul study finds

Radiation therapy following breast cancer surgery does not increase the risk of developing skin cancer, according to a new South Korean study.

A research team led by Professor Yoon Chang-ik of the Breast Cancer Center at the Cancer Hospital of Seoul St. Mary's Hospital, Catholic University of Korea, analyzed long-term follow-up data on breast cancer surgery patients using national health insurance claims data and found no significant difference in skin cancer risk based on whether patients received radiation therapy. Professors Jin Je-hyeon and Kim Du-re of the Breast Surgery Department served as co-first authors.

Breast cancer is diagnosed in approximately 30,000 women in South Korea each year. For early-stage cases, radiation therapy is often administered after breast-conserving surgery to eliminate any remaining cancer cells.

However, concerns have persisted that radiation exposure could raise the long-term risk of skin cancer. Previous studies conducted on Western populations reported that breast cancer patients who received radiation therapy faced a 12 to 57 percent higher risk of skin cancer than those who did not. Large-scale research on Asian populations had been lacking.

The research team drew from patients diagnosed with breast cancer between 2009 and 2012 who were at least 20 years old, accounting for surgical history and prior cancer or treatment records, and arrived at a final analysis group of 37,957 patients. They then matched patients by age, sex and treatment history to compare 9,928 patients in the radiation therapy group against 9,928 in the non-radiation group, for a total of 19,856 patients.

The analysis found skin cancer incidence rates of 0.97 percent in the radiation therapy group and 1.02 percent in the non-radiation group — in effect no difference. When broken down into melanoma and other skin cancers, no meaningful difference in risk was found based on radiation therapy status. The average follow-up period was about 11.5 years, or 138 months.

By contrast, older age, the presence of moles, precancerous skin lesions such as actinic keratosis and Bowen's disease, and lymphedema were all associated with higher skin cancer risk.

Patients with moles faced a skin cancer risk 5.3 times higher than those without. The risk was 12.9 times higher in patients with precancerous skin lesions and about twice as high in those with lymphedema.

The research team attributed the divergence from Western studies to racial differences and advances in radiation therapy technology. They also noted that patients in this study were treated during a period when three-dimensional conformal radiation therapy (3D-CRT) had become established practice, which may have reduced incidental damage to healthy skin.

The study has limitations, however: radiation-induced skin cancer can appear 20 or more years after exposure, meaning the findings alone cannot confirm long-term safety. The research team said follow-up studies with longer observation periods are needed.

"This study is significant in that it directly examined outcomes for tens of thousands of patients who actually received treatment, using national health insurance claims data," Professor Jin said. "We hope breast cancer patients can set aside vague anxieties about skin cancer and focus on completing their radiation therapy."

"This research provides evidence that the radiation therapy methods used today do not significantly elevate skin cancer risk," Professor Yoon said. "It is important to develop systematic strategies for screening and managing patients with high-risk skin conditions such as moles, precancerous lesions and lymphedema."

The study was published in the British Journal of Cancer.