(HealthDay News) – Changes in size on sequential low-dose computed tomography (LDCT) screenings, expressed as volume doubling time (VDT), indicate that about 25% of progressive lung cancers are slow growing or indolent, with higher lung cancer-specific mortality for new vs. slow-growing or indolent cancers, according to a study published in the Dec. 4 issue of the Annals of Internal Medicine.

Giulia Veronesi, MD, from the European Institute of Oncology in Milan, and colleagues assessed VDT as an indicator of overdiagnosis for screening-detected lung cancer by estimating the VDT in 175 high-risk patients who were diagnosed with primary lung cancer. VDT was characterized as fast growing (VDT <400 days), slow growing (VDT between 400–599 days), or indolent (VDT ≥600 days).

Within the cohort, 55 cases of cancer were diagnosed at baseline and 120 were diagnosed subsequently. Of the later group, the researchers found that 15.8% of tumors were not visible on previous scans and were classified as fast growing (median VDT 52 days); 84.2% were progressive (58.3% fast growing and 25.8% slow growing [15%] or indolent [10.8%]). For patients with new versus slow-growing or indolent cancer, lung cancer-specific mortality was significantly higher (9.2% vs. 0.9% per year). Of the incident cancers, 60% of fast-growing progressive cancer and 45% of new cancers were Stage 1.

“Slow-growing or indolent cancer comprised approximately 25% of incident cases, many of which may have been overdiagnosed,” the authors write. “To limit overtreatment in these cases, minimally invasive limited resection and nonsurgical treatments should be investigated.”

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