In medium-size pathology practices without sub-specialization and a modest volume of lung biopsies, small cell carcinoma may be a diagnosis that is seen by the individual pathologist once or twice a year. In such environments, where the working diagnosis is small cell carcinoma but the TTF-1 immunostain is negative, an external consultation may be sought due to uncertainty about the tumor sub-type. Prior (unpublished) work showed that individual pathologists in our thoracic referral center diagnose only two to three small cell carcinomas on lung core biopsies per year. Here, TTF1 is linked to small cell carcinoma.