Classification of Lung Tumors: An Overview of Lung Carcinomas

Abstract

In the last few decades classification of lung tumors has been revised several times. The first classification was proposed by the World Health Organization (WHO) in 1967 and was revised 14 years later in 1981. A major change was proposed in subclassification of small cell carcinoma in 1988 by the pathology panel of the International Association for the Study of Lung Cancer (IASLC). The most recent classification, referred to as the WHO/IASLC Histologic Classification of Lung and Pleural Tumors, was published in 1999. The new classification was deemed necessary because of vast progress made in understanding the clinical, epidemiological, histogenetic, and molecular aspects of lung cancers. The current classification (Table 5–1) is notable in the following respects:

• Addition of preinvasive categories for glandular and neuroendocrine neoplasia.

• Revision of the small cell carcinoma category by eliminating the subtypes of oat cell and intermediate cell types and retaining only one variant, combined small cell carcinoma. The revised classification also does not include the category of small and large cell type as was proposed by IASLC in 1988.

• Addition of new category for spindle cell/giant cell carcinomas, which includes all malignancies consisting of spindle and giant cell components, carcinosarcomas, and pulmonary blastomas.

• Addition of several new variants of adenocarcinomas.

• Inclusion of large cell neuroendocrine carcinomas as a variant of large cell carcinomas.