Prognostic Implications of the Volume Doubling Time of the Solid Component in Lung Adenocarcinomas Manifesting as Part-Solid Lesions on Chest CT

Background: In lung adenocarcinomas manifesting as part-solid lesions, evidence supports greater prognostic importance for the volume of the solid component than of the whole nodule. However, assessments of lesion growth rates have historically focused on the volume doubling time (VDT) of the whole lesion. Objective: To compare the prognostic utility of the VDT of the solid component versus of the whole lesion for resected lung adenocarcinomas manifesting as part-solid lesions on chest CT. Methods: This retrospective study included 122 patients (mean age, 64.0 ± 8.2years; 53 men, 69 women) with resected lung adenocarcinoma manifesting as a part-solid lesion who underwent at least two preoperative chest CT examinations showing either solid-component growth or at least 2 years of stability. Semiautomated software was used to perform 3D segmentations of whole lesions and their solid components, to derive corresponding whole-lesion and solid-component volumes. These volumes were used to compute for each patient VDT for the whole lesion (VDTw) and the lesion's solid component (VDTs). In 81 patients in whom the lesion's ground-glass component increased, VDT of the ground-glass component (VDTgg) was calculated, subtracting the solid-component volume from whole-lesion volume to derive the ground-glass component volume. The prognostic utility of VDTw, VDTs, and VDTgg (each as continuous variables and as binary variables at 200-day and 400-day cutoffs) for recurrence-free survival (RFS) and overall survival (OS) were evaluated using Cox proportional hazard models, adjusting for age, sex, and clinical variables associated with lung cancer survival. Results: Median VDTw, VDTs, and VDTgg, were 921, 455, and 1000 days, respectively. The only VDT metrics showing significant independent associations with RFS were VDTs as a continuous variable (HR=0.999; p=.02), VDTs <400 days (HR=2.68; p=.03), and VDTs <200 days (HR=3.68; p=.003). The only VDT metrics showing significant independent associations with OS were VDTs <200 days (HR=3.27; p=.047) and VDTw <200 days (HR=4.86; p=.03). Conclusion: In lung adenocarcinomas manifesting as part-solid lesions, VDTs less than 200 days was the only evaluated VDT metric showing significant independent associations with both RFS and OS. Clinical Impact: The findings support a focus on lesions' solid components when assessing growth rates of part-solid lesions.