Apr. 17, 2007 Every day, people make assumptions, educated and not, about their risk for developing cancer. For many, the risk of developing a secondary cancer after an earlier illness rests uncomfortably in the backs of their minds. Researchers are continuing to understand the factors that might dictate an individual's risk of developing primary or secondary cancer. The risk of developing cancer depends on the subtle interplay of genetics, personal choice and the environment, according to large-scale recent studies.
A team of 19 researchers from Australia, Canada, Iceland, Singapore, and several European countries has completed what they call the "largest population-based study of absolute and relative risk of second malignant neoplasms (SMNs)" in childhood leukemia and lymphoma survivors. The study, which analyzed data from 13 cancer registries in several countries, found that these survivors have a higher-than-average risk of developing a different type of cancer later in life.
"Large-scale, long-term population studies are necessary to have a better understanding of the risk of second primaries among cancer patients," said study coordinator Paolo Boffetta, M.D., MPH, of the International Agency for Research on Cancer. "Most of the second primary cancers after a childhood cancer are, fortunately, rare. One therefore needs large series of patients to precisely estimate risks."
The registries used had been active for at least 25 years and covered different time periods between 1943 and 2000. Each provided individual data on leukemia, Hodgkin's lymphoma, and Non-Hodgkin's lymphoma, along with second cancers -- new primaries, not recurrences or metastases -- in children from infancy through age 14. The researchers' analysis found that the cumulative incidence of second cancers was 2.43 percent, 12.7 percent, and 2.5 percent within 30 years since leukemia, Hodgkin's lymphoma and Non-Hodgkin's lymphoma, respectively.
According to the researchers, this means that survivors of these childhood cancers are considered to be "high risk" for developing second cancers. This is especially true for Hodgkin's lymphoma survivors: one in eight was affected within 30 years from the initial diagnosis.
"This is probably due to the better survival of Hodgkin's lymphoma patients who received highly toxic chemotherapy, as compared to other groups of patients," Boffetta said. "In other words, chemotherapy, possibly in combination with radiotherapy, increased the survival of Hodgkin's lymphoma patients but also their risk of developing a second cancer."
In Hodgkin's lymphoma survivors, researchers observed an increased risk for brain, thyroid, breast, and nonmelanoma skin cancer, as well as leukemia.
The study could not assess whether risk of a second cancer varied among children who were treated in the 1940s, 50s, or 60s versus more recent decades, due to the limited follow-up time for the latter population. According to Boffetta, their risk estimates are based on patients who had past treatment regimens -- those for whom they have enough follow-up to make proper estimates. Those estimates may not reflect the risk entailed by more recent, and presumably less toxic, regimens.
"The significance of these results for adult survivors of childhood cancers is that they provide a more precise estimate of their risk of developing a second primary cancer," Boffetta said.
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