A grading system for pulmonary adenocarcinoma has not been established. This study was done to evaluate a set of histologic criteria associated with prognosis aimed at establishing a grading system for invasive pulmonary adenocarcinoma.
A multi-institutional study involving multiple cohorts of invasive pulmonary adenocarcinomas was conducted. A cohort of 284 stage I pulmonary adenocarcinomas was used as a training set to identify histologic features associated with patient outcomes. Receiver operating characteristic curve analysis was used to select the best model, which was validated and tested in independent cohorts. The reproducibility of the model was assessed using kappa statistics.
The best model was composed of a combination of predominant plus high-grade histologic patterns with a cutoff of 20% for the latter. The model consists of grade 1, lepidic predominant tumor; grade 2, acinar or papillary predominant tumor, both with no or less than 20% of high-grade patterns; and grade 3, any tumor with 20% or more of high-grade patterns.
This study provided a grading system based on the predominant and high-grade patterns that are practical and prognostic for invasive pulmonary adenocarcinoma.