FIG 4.

A 62-year-old man with lung adenocarcinoma treated with first-line pembrolizumab. Baseline computed tomography before starting pembrolizumab showed a right lower lobe lung mass contiguous from the hilum, measuring 5.3 cm (A, arrow). On the initial follow-up scan at 1.5 months of therapy, the tumor measured 6.4 cm (B, arrow), demonstrating 21% increase compared with the baseline and meeting the criteria for progressive disease by RECIST1.1. However, the subsequent scans demonstrated tumor shrinkage (C at 4.5 months and D at 12 months as representative scans), later achieving ≥ 30% decrease compared with the baseline at 14 months of therapy (E) when it measured 3.2 cm (40% decrease since the baseline). Further decrease was noted on the consecutive follow-up scans at 16 months (F), confirming response. The tumor burden continued to remain small on the subsequent follow-up scans, and the patient remained progression-free at 21 months of therapy. Asterisks demonstrate postobstructive atelectasis that is not included in the tumor burden measurement.