Cancer conversion rates at 3 and 12 months interval scans in a lung cancer screening programme

<bold>Title:</bold> Cancer conversion rates at 3 and 12 months interval scans in a lung cancer screening programme <bold>Introduction:</bold> In patients undergoing a lung cancer screening low-dose CT (LDCT), 15% will have a nodule requiring an early interval CT. We aimed to understand the cancer conversion rates at 3 and 12 months. <bold>Methods:</bold> We reviewed LDCT outcomes from a single site performing 640 scans/month between August 2022 and February 2024. Of note, nodules identified at baseline were compared with prior imaging where available, thereby reducing the recommended interval scanning in 1 in 8 patients. <bold>Results:</bold> Over the 18-month period 674/8304 (8.1%) index LDCT scans had nodules requiring follow up at 3 months. The median time between baseline and 3-month interval scan was 89[IQR 82-102] days. At 3 months, 54/ 674 (8%) scans were alerted for further evaluation of which 8/674(1.2%) had lung cancer. Of these, 6(75 %) were stage I at diagnosis and the remaining two cases were stage II and stage IV. In the stage IV case, the histopathology confirmed small cell lung cancer. The decision for interval CT scans was due to the index nodule having some characteristics of a hamartoma. However, with hindsight, a 4L mediastinal lymph node was present. A stage shift from IIIb to IV occurred. Over this period only 23 participants had a 12 month interval scan. Of these, five scans were alerted and two confirmed as lung cancer. <bold>Conclusion:</bold> The risk of cancer was found to be 1.2% at 3 months with 87 % being early-stage. Our data was limited for the 12 month conversion rate.