Invasive adenocarcinoma of lung, acinar type. Irregularly-shaped glands are present in a fibrotic stroma. This case also showed smaller foci of papillary and lepidic growth patterns. According to the WHO 2015 classification of lung tumors, the different histologic components in a resected lung adenocarcinoma should be assessed semi-quantitatively in 5% increments by careful evaluation of submitted sections. The tumor is classified based on the predominant component present (acinar in this case). Each of the other components are documented in the report due to prognostic implications.