Most of these studies did not take into account the differences in tumor subtype or histology, which is a limitation given that lung ADC consists of a heterogeneous group of neoplasms with varying biologic behavior and prognosis.10,30 Beginning with the landmark study by Noguchi et al,31 and corroborated by others, it was recognized that tumors with essentially pure lepidic growth had nearly 100% 5-year survival, an outcome markedly distinct from the majority of lung ADC. Based on this observation, the WHO in 1999 and 200411 defined what was then called bronchioloalveolar carcinoma (BAC) as a tumor with pure lepidic growth. Still, the majority of ADCs were classified as “mixed type” in the 2004 WHO classification, the category of ADC that encompassed the largest group of tumors, and which, by their diversity, possessed variable biologic behavior.32 Because these tumors have heterogeneous clinical, molecular, pathologic, and radiologic characteristics, the mixed category provided minimal practical information to the clinician regarding potential prognosis.10 To address the clinical need for a prognostic relevance, a multidisciplinary consensus classification was published jointly by the IASLC, ATS, and ERS in 2011 that included a reclassification of tumors with pure lepidic growth as AIS replacing the terminology of BAC.10 Second, a category of MIA was introduced based on data10,31 indicating that lepidic tumors with an invasive component equal to or < 5 mm have essentially the same survival as those with pure lepidic growth. The final major change was the elimination of the mixed category with the recommendation that ADC be categorized by the predominant histologic subtype (ie, lepidic, papillary, acinar, solid, or micropapillary) (Table 1). The intent was to provide clinical, that is, prognostic meaning to the former mixed category. Most studies have demonstrated the prognostic value in this classification system, with favorable (lepidic), intermediate (acinar and papillary), and poor (solid, micropapillary) prognostic categories.30,32‐34 The results of our pilot study corroborate prior data and demonstrated prognostic stratification based on tumor histology.