The New IASLC-ATS-ERS Lung Adenocarcinoma Classification: What the Surgeon Should Know

Abstract

In 2011, a new histologic classification of lung adenocarcinomas was proposed from a joint working group of the International Association for the Study of Lung Cancer (IASLC), American Thoracic Society (ATS), and European Respiratory Society (ERS), based on the recommendation of an international and multidisciplinary panel. This classification proposed a method of comprehensive histologic subtyping (lepidic, acinar, papillary, micropapillary, and solid pattern) based on semi-quantitative assessment of histologic patterns (in 5% increments) with the ultimate goal of choosing a single, predominant pattern. Prognostic subsets could then be described for the classification. Patients with completely resected adenocarcinomas in situ (AIS) and minimally invasive adenocarcinomas (MIA) experienced low risk of recurrence. Patients with micropapillary or solid predominant tumors have a high risk for recurrence or cancer-related death. Patients with acinar and papillary predominant tumors comprise an intermediate-risk group. Herein, we review the outline of the proposed IASLC/ATS/ERS classification, a summary of published validation studies of this new classification and then discuss surgical key issues; we mainly focused on limited resection as an adequate treatment for early-stage lung adenocarcinomas as well as pre- and intraoperative diagnoses. We also review the published studies that identified the importance of histological subtypes in predicting recurrence, both rates and patterns, in early-stage lung adenocarcinomas. This new classification for the most common type of lung cancer is useful for surgeons, as its implementation would require only hematoxylin and eosin (H&E) histology slides, which is the common type of stain used in hospitals. It can be implemented with routine pathology evaluation and with no additional costs.

Clinicopathological characteristics and prognosis of non-lepidic invasive adenocarcinoma presenting as ground glass opacity nodule

“…Prior studies have shown outcomes of 100% RFS after surgical resection for AIS and MIA, and among the five subtypes of adenocarcinoma, lepidic adenocarcinoma showed the most favorable prognosis (14,15). Some reports also determined that the degree of lepidic pattern in a tumor was related to disease prognosis, where greater than 50% lepidic pattern was a favorable prognostic indicator in cases of invasive adenocarcinoma (16)(17)(18).…”

“…One of those indications is for nodules with greater than 50% GGO appearance on CT. Moreover, two ongoing studies (JCOG 0802, JCOG 0804) have also adopted C/T ratio to select sublobar resection (14,22). Clinically, it is practical for thoracic surgeons to use the C/T ratio to classify nodules on CT as GGO-predominant or solid-predominant.…”

Risk factors for recurrence after sublobar resection in patients with small (2 cm or less) non-small cell lung cancer presenting as a solid-predominant tumor on chest computed tomography

“…One recent study using a national cancer database in the United States demonstrated that patients who underwent sublobar resection for stage IA NSCLC had poorer oncologic outcomes (14). However, some studies reported that patients who had sublobar resection for stage IA NSCLC presenting as a GGO nodule had similar oncologic outcomes (6,7,15). Therefore, it might be possible that sublobar resection is suitable for selective cases.…”

“…In this study, we evaluated RFS instead of overall survival because with stage I disease, more patients succumbed to other causes than from cancer during the follow-up period (7). Further, RFS is a more accurate measurement of survival, as it reflects the biological behavior of the cancer rather than death secondary to unrelated factors.…”

“…Many studies have demonstrated that patients had a good prognosis after sublobar resection for GGO-predominant nodules (5)(6)(7). Accordingly, sublobar resection for GGOpredominant tumors is considered reasonable treatment.…”