Although the risk of subsequent malignancies for survivors of childhood cancer diagnosed in the 1990s remains increased, the risk is lower compared with those diagnosed in the 1970s, a decrease that is associated with a reduction in therapeutic radiation dose, according to a study appearing in the February 28 issue of JAMA.

The Childhood Cancer Survivor Study and other groups of childhood cancer survivors have reported extensively on the incidence of and risk factors for subsequent neoplasms (tumours).

Therapeutic radiation has been strongly associated with development of subsequent tumours; however, links have also been identified between specific chemotherapeutic agents and the development of tumours.

With this information, childhood cancer treatment has been modified over time with the hope of reducing subsequent tumour risk, while maintaining or improving 5-year survival.

Lucie M. Turcotte, M.D., M.P.H., M.S., of the University of Minnesota Medical School, Minneapolis, and colleagues conducted a study that included 23,603 five-year cancer survivors (average age at diagnosis, 7.7 years) from paediatric hospitals in the United States and Canada between 1970-1999, with follow-up through December 2015.

Between the 1970s and the 1990s, the percentage of pediatric cancer patients treated with radiation fell from 77 to 33 percent.

During an average follow-up of 20.5 years, 1,639 survivors experienced 3,115 subsequent neoplasms.

The most common subsequent malignancies were breast and thyroid cancers.

Proportions of individuals receiving radiation decreased (77 percent for 1970s vs 33 percent for 1990s), as did median dose.

Fifteen-year cumulative incidence of subsequent malignancies decreased by decade of diagnosis (2.1 percent for 1970s, 1.7 percent for 1980s, 1.3 percent for 1990s).

Relative rates declined with each 5-year increment for subsequent malignancies.

Radiation dose changes were associated with reduced risk for subsequent malignancies, meningiomas (a tumour that arises from the membranes that surround the brain and spinal cord), and nonmelanoma skin cancers.

"The current analysis, including more than 23,000 survivors of childhood cancer treated over 3 decades, demonstrated that the cumulative incidence rates of subsequent neoplasms, subsequent malignant neoplasms, meningiomas, and nonmelanoma skin cancers were lower among survivors treated in more recent treatment eras and that modifications of primary cancer therapy were associated with these declines," the authors write.

"The most ominous late effect of pediatric cancer treatment is a second malignancy," said Gregory Armstrong, MD, of the St. Jude Department of Epidemiology and Cancer Control, head of the study "This study shows efforts to reduce the late effects of treatment are paying off.

"The risk of second cancers for survivors increases with age, so it is good to see the reduction emerging early in survivorship while survivors are still young."

Source: JAMA and St Jude Children's Research Hospital