Understanding the fundamental nature of the risks is an active area of research, and one that's moved on significantly with the publication of a new report that provides a quantitative analysis of radiation exposure during therapy and the incidence of subsequent tumours of the central nervous system (CNS) in survivors of childhood cancer (J. Natl Cancer Inst. 98 1528). The work was carried out as part of the US Childhood Cancer Survivor Study (CCSS), an ongoing programme that is tracking more than 14,000 five-year survivors of childhood cancer in an effort to quantify the incidence of late effects of childhood cancer and its treatment.

In this latest CCSS research programme, Joseph Neglia, a paediatric oncologist at the University of Minnesota Medical School and Cancer Center in Minneapolis, and colleagues demonstrated a "strong and statistically significant association" between radiation therapy and the subsequent occurrence of CNS tumours. What's more, their analysis also included the reconstruction of radiation dose to the site of the CNS tumour, which allowed them to elucidate the dose-response relationships and the expression of excess risk over time.

In their paper, Neglia and co-workers report on 116 childhood cancer survivors from the CCSS cohort who developed subsequent malignant and benign tumours of the CNS. "Each patient was matched with four control subjects by age, sex and time since original cancer diagnosis," write the authors. "Tumour site-specific radiation dosimetry was performed, and chemotherapy information was abstracted from medical records."

After crunching through the data, the researchers arrived at three headline conclusions. First, exposure to radiation therapy is the single most important risk factor for the development of a new CNS tumour in survivors of childhood cancers. Second, after adjustment for radiation dose, neither original cancer diagnosis nor chemotherapy was associated with the risk of CNS tumours. And finally, the higher risk of subsequent glioma in children irradiated at a very young age (before age five) may reflect greater susceptibility of the developing brain to radiation.

In an accompanying editorial, Elaine Ron of the National Cancer Institute (Bethesda, MD), puts the findings into context. "It is important to increase our understanding of secondary cancers and what factors affect risk," she explains. "By identifying persons at high risk of long-term effects, it may be possible to reduce the growing number of patients who develop secondary malignancies by individualizing treatments."

Clearly, working towards this goal requires long-term financial and resource commitment from both the public and private sectors. It also requires a collective effort, one that brings together medical physicists (in research and clinical practice), radiation oncologists, paediatricians, statisticians and other healthcare professionals. This multidisciplinary endeavour is all the more pressing given rapid technological advances in cancer treatment - intensity-modulated radiation therapy being a case in point - and related concerns about the possible higher incidence of radiation-associated second cancers versus conventional radiation therapies.