By Lynda Williams, Senior medwireNews Reporter
Patients treated for primary choroidal or ciliary body melanoma may not always benefit from an aggressive surveillance strategy for the detection of metastatic disease, caution US researchers.
The team from the University of California at San Francisco found that the risk for a secondary radiation-induced cancer from regular positron emission tomography (PET) or computed tomography (CT) could outweigh the risk for recurrent disease in younger individuals.
Tara McCannel and co-workers used data from the Biological Effects of Ionizing Radiation VII report to calculate the lifetime attributable risk (LAR) for cancer associated with different PET or CT surveillance protocols for patients of different ages.
As reported in JAMA Ophthalmology, annual head, abdomen and pelvic CT for 10 years in 50-year-old male and female patients had estimated LARs for a secondary cancer of 0.9% and 1.3%, respectively, rising to 1.8% and 2.5% with scans at 6-month intervals.
For annual whole-body PET or CT over 10 years in a 50-year old man or women, the LAR for secondary cancer are 1.6% and 1.9%, respectively, increasing to 3.3% and 3.9% when conducted at 6-month intervals.
For younger patients, the risks were significantly greater, with the LAR for secondary cancer for a man or a woman aged 20 rising to 5.0% and 7.9%, respectively, for whole-body PET or CT scans at 6-month intervals for 10 years.
Despite the absence of evidence-based guidelines demonstrating increased survival with aggressive surveillance, some clinicians recommend annual or biannual whole-body CT or PET scans, or head, abdomen and pelvis CT to monitor patients with choroidal melanoma.
With approximately a third of patients developing untreatable metastases within 10 years, the researchers admit that the 50% mortality rate for the malignancy, and the time lag associated with radiation-induced cancer, means that the LARs for secondary cancer with imaging may not be an issue for many patients.
As prognosis is dependent on age and chromosomal markers, however, the team believes that the risks for secondary radiation-induced cancers should be considered when scheduling surveillance. Serial magnetic resonance imaging could potentially be the "safer option" for younger, lower-risk patients, with PET or CT reserved for follow up on abnormal lesions.
"For an older individual with a poor prognosis and high risk for metastatic disease, an aggressive protocol may have the benefits of detecting metastases earlier and enabling initiation of treatment or enrollment in a treatment trial sooner, which may outweigh the risks," McCannel et al say.
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