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IMRT for prostate cancer does not increase risk for leukemia, myelodysplasia
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Intensity-modulated radiation therapy for the treatment of prostate cancer did not increase the risk for leukemia or myelodysplasia compared with 3-dimensional conformal radiotherapy, according to results of a retrospective cohort study.
Further, patients treated with IMRT experienced reduced risk for colon and rectal cancers.
“IMRT is commonly used for patients with prostate cancer because it allows dose escalation to the tumor while reducing radiation exposure to the surrounding healthy tissues, such as the bladder and rectum,” Neige M.Y. Journy, PhD, MPH, postdoctoral fellow in the radiation epidemiology branch in the division of cancer epidemiology and genetics at NCI, and colleagues wrote. “This reduction may be at the expense of increased radiation exposure to more distant tissues form scatter radiation, particularly the red bone marrow, compared with the exposure from 3-dimensional conformal radiotherapy (3D-CRT), the previous standard radiotherapy technique.”
Journy and colleagues evaluated risks for leukemia and myelodysplasia — which can be caused by higher bone marrow dose and can occur as early as 2 years after exposure — as well as second solid cancers.
Researchers used the SEER–Medicare database to identify 39,028 patients aged 66 to 84 years who were diagnosed with nonmetastatic prostate cancer between 2002 and 2009. Patients had received IMRT (n = 27,904) or 3D-CRT (n= 11,124) within the first year following diagnosis, did not receive chemotherapy and survived at least 2 years after treatment initiation.
Researchers followed patients from radiotherapy initiation until the second cancer diagnosis, death, patient age reached 90 years or Dec. 31, 2011.
During a median follow-up of 5.2 years (range, 2 to 10), 2,901 men developed second cancers, including 6.1% (n = 1,691) of the IMRT group and 10.9% (n = 1,210) of the 3D-CRT group.
Men who underwent IMRT did not demonstrate an increased risk for all leukemia and myelodysplasia compared with men who underwent 3D-CRT (RR = 0.86; 95% CI, 0.86-1.09). This trend persisted when researchers evaluated non-chronic lymphoblastic leukemia (RR = 0.89; 95% CI, 0.62-1.28) and myelodysplasia (RR = 1.03; 95% CI, 0.72-1.48) separately.
However, patients treated with IMRT demonstrated decreased risks for colon cancer (RR = 0.59; 95% CI, 0.43-0.81) and rectal cancer (RR = 0.58; 95% CI, 0.36-0.93).
Risks for other solid cancers and lymphomas did not differ significantly between IMRT and 3D-CRT.
Receipt of chemotherapy, brachytherapy, hormonal therapy and surgery did not significantly affect results, and the associations persisted in sensitivity analyses.
“No association of radiotherapy mortality with lung cancer risk was observed, suggesting that residual confounding by smoking is unlikely to account for the inverse associations observed for colon and rectal cancer,” Journy and colleagues wrote. “The study had sufficient follow-up to evaluate early incidence of leukemia and myelodysplasia, which might occur as soon as 2 years after radiation exposure, but was currently limited to evaluate the risk [for] solid cancer, which usually occur 5 to 10 years after radiation exposure,” they wrote.
Longer follow-up is needed, they wrote. – by Nick Andrews
Disclosure: The researchers report no relevant financial disclosures.
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