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

<b>BACKGROUND.</b> In lung adenocarcinomas manifesting as part-solid lesions, evidence supports greater prognostic importance for the volume of the solid component than that of the whole nodule. However, assessments of lesion growth rates have historically focused on the volume doubling time (VDT) of the whole lesion. <b>OBJECTIVE.</b> The purpose of the study was to compare the prognostic utility of the VDT of the solid component versus the VDT of the whole lesion for resected lung adenocarcinomas manifesting as part-solid lesions on chest CT. <b>METHODS.</b> This retrospective study included 122 patients (mean age, 64.0 ± 8.2 [SD] years; 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; these segmentations were used to derive corresponding whole-lesion and solid-component volumes. These volumes were used to compute for each patient VDT of the whole lesion (VDT_w) and VDT of the solid component (VDT_s). In 81 patients in whom the lesion's ground-glass component increased, VDT of the ground-glass component (VDT_gg) was calculated, subtracting the solid-component volume from the whole-lesion volume to derive the ground-glass component volume. The prognostic utility of VDT_w, VDT_s, and VDT_gg (each as continuous variables and as binary variables at 200- and 400-day cutoffs) for recurrence-free survival (RFS) and overall survival (OS) were evaluated using Cox proportional hazards models, adjusted for age, sex, and clinical variables associated with lung cancer survival. <b>RESULTS.</b> Median VDT_w, VDT_s, and VDT_gg were 921, 455, and 1000 days, respectively. The only VDT metrics showing significant independent associations with RFS were VDT_s as a continuous variable (HR = 0.999; <i>p</i> = .02), VDT_s of less than 400 days (HR = 2.68; <i>p</i> = .03), and VDT_s of less than 200 days (HR = 3.68; <i>p</i> = .003). The only VDT metrics showing significant independent associations with OS were VDT_s of less than 200 days (HR = 3.27; <i>p</i> = .047) and VDT_w of less than 200 days (HR = 4.86; <i>p</i> = .03). <b>CONCLUSION.</b> In lung adenocarcinomas manifesting as part-solid lesions, VDT_s of less than 200 days was the only evaluated VDT metric that showed significant independent associations with both RFS and OS. <b>CLINICAL IMPACT.</b> The findings support a focus on lesions' solid components when assessing growth rates of part-solid lesions.