The accuracy of the histological classification of lung carcinoma and its reproducibility: a study of 75 archival cases of adenosquamous carcinoma.

The classification of lung carcinoma into a small cell lung carcinoma (SCLC) and non-small cell lung carcinoma (NSCLC), is highly reproducible. There are few studies on the reproducibility of subtyping NSCLC, with anecdotal reports on the subtype of adenosquamous carcinoma. We undertook a study of 75 cases archived as adenosquamous carcinoma. All cases were accepted as NSCLC on independent review by three pathologists utilizing the 1982 World Health Organization (WHO) classification criteria. The acceptance rate of adenosquamous carcinoma by the three pathologists was 65%, 28%, and 65%. Cases not accepted as adenosquamous fell into the different subtypes of NSCLC, with a concordance rate between each pair of pathologists of 49%, 61% and 43%, indicating poor agreement between pathologists. The study confirms the high reproducibility of the classification into SCLC and NSCLC; it shows poor concordance for all subtypes of NSCLC with poor reproducibility of diagnosis of adenosquamous carcinoma as specified by the 1982 WHO classification. Physicians dealing with lung carcinoma should be aware of this limitation of classification.