Association between the baseline tumor size and outcomes of patients with non-small cell lung cancer treated with first-line immune checkpoint inhibitor monotherapy or in combination with chemotherapy

Background: The baseline tumor size (BTS) is a prognostic factor for patients with non-small cell lung cancer (NSCLC) who received immune checkpoint inhibitor monotherapy (ICI-mono). However, this relationship is not yet known in patients treated with ICI in combination with chemotherapy (ICI-chemo). Methods: This single-center retrospective study evaluated 159 patients with advanced NSCLC who received first-line ICI-mono or ICI-chemo from January 2016 to April 2021. Their BTS values were estimated using the maximum BTS (max BTS) (maximum target lesions' longest diameter) and total BTS (sum of target lesions' longest diameters) in a radiological assessment according to the Response Evaluation Criteria for Solid Tumors. Results: Based on a multivariable analysis, the large max BTS group had worse progression-free survival (PFS) in patients treated with ICI-mono (P=0.009), but it was not associated with worse PFS in patients treated with ICI-chemo (P=0.132). The group treated with ICI-mono had worse PFS compared to the group treated with ICI-chemo in patients with max BTS >= 50 mm (P=0.004), and the group treated with ICI-mono was not associated with worse PFS compared to the group treated with ICI-chemo in patients with max BTS <50 mm (P=0.107). Conclusions: While a large max BTS was identified as a prognostic factor for worse PFS in patients treated with ICI-mono, it was not identified as such in patients treated with ICI-chemo. The max BTS may have different predicting efficacy for patients with NSCLC treated with ICI-mono and ICI-chemo.