In which of the following forms of pulmonary carcinoma is the classic progression of metaplasia to dysplasia to carcinoma in situ observed: (A) Small-cell carcinoma, (B) Adenocarcinoma, (C) Large-cell carcinoma, (D) Squamous cell carcinoma
Answer is D. All stages from squamous metaplasia to carcinoma in situ are observed in squamous cell carcinoma. Such a clear progression is not seen in the other forms of cancer listed.