In the study, simple cysts never indicated the presence of cancer. Such thyroid cysts should be considered "essentially never malignant" and should not be biopsied, Dr. Smith-Bindman and her associates said.
"The main strength of our study is the large sample size and the linkage of the cohort with data from a comprehensive cancer registry, which allows accurate assessment of the true underlying prevalence of cancer," the researchers noted.
The overall prevalence of primary thyroid cancer was 1.5% in the study population. In contrast, most previous studies have cited a prevalence rate closer to 20%. "All previous studies have inflated the association between nodule characteristics and cancer risk because they limited their analyses to nodules that underwent biopsy," the investigators said.
The National Cancer Institute and the University of California, San Francisco, supported the study. No financial conflicts of interest were reported.
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