MedWire News: The majority of second solid cancers occurring in breast cancer survivors are not related to radiotherapy, indicate findings of a large population-based study in the USA.
“Radiotherapy for breast cancer reduces disease recurrence and breast cancer mortality. However, it has also been associated with increased second cancer risks in exposed sites,” remark Amy Berrington de Gonzalez (National Cancer Institute, Bethesda, Maryland, USA) and colleagues.
In the present study, Berrington de Gonzalez and team evaluated the long-term risk for second cancer among 182,057 women with locoregional invasive breast cancer diagnosed between 1973 and 2000. All the women included in the study had survived for at least 5 years after the initial cancer diagnosis.
During a median follow-up period of 13 years, a total of 15,498 women developed a second primary solid cancer, including 6491 contralateral breast cancers.
The researchers found that the incidence of esophageal, pleural, bone, soft tissue, and contralateral breast cancer among women treated with surgery plus radiotherapy was more than double what would be expected in the general female population.
Women who under underwent surgery plus radiotherapy had a 9% increased risk for contralateral breast cancer, compared with surgery alone. Those who received high dose (1 Gy or more) radiotherapy had a 45% increased risk for esophageal, pleural, bone, and soft tissue cancer compared with women who just had surgery.
These risks decreased with increasing age and year of treatment and there was no evidence of elevated risks for sites receiving medium (0.5–0.99 Gy) or low (below 0.5 Gy) radiation doses.
Berrington de Gonzalez and team estimated that there were 176 excess cases of contralateral breast cancer in women who had surgery plus radiotherapy, which amounts to 5% of the contralateral breast cancers diagnosed in 1-year survivors. Among the same group of women, there were an estimated 292 (6%) excess cases of solid cancers (other than contralateral breast cancer).
“Our findings suggest that most second solid cancers after treatment for breast cancer are related to other risk factors such as lifestyle or genetic factors,” conclude Berrington de Gonzalez et al in the British Journal of Cancer.
MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010
Free abstract
