Pulmonary Adenocarcinoma Updates: Histology, Cytology, and Grading

Context.— Adenocarcinomas are the most common histologic subtype of lung cancer, and exist within a widely divergent clinical, radiologic, molecular, and histologic spectrum. There is a strong association between histologic patterns and prognosis that served as the basis for a recently described grading system. As the study of molecular pathology rapidly evolves, all targetable mutations so far have been found in adenocarcinomas, thus requiring accurate diagnosis and classification for the triage of molecular alterations and adequate therapy. Objective.— To discuss the rationale for adenocarcinoma classifications within the 2021 5th edition of the World Health Organization Classification, with a focus on nonmucinous tumors, including tumor grading and biopsy/cytology diagnosis. Data Sources.— PubMed search. Conclusions.— A grading system for adenocarcinoma has improved prognostic impact of the classification of pulmonary adenocarcinoma. An accurate diagnosis of adenocarcinoma in small biopsy material is important for tissue triage for molecular studies and ultimately for patient management and treatment.