The sequential development of cancer: a morphological perspective

Cancer development proceeds through sequential or contemporaneous morphological changes from normal, preneoplastic, and premalignant lesions to highly malignant neoplasms. The morphological continuum that comprises cancer development is usually divided into diagnostic categories of hyperplasia (or dysplasia), benign neoplasia, and malignant neoplasia based on perceived biological behavior. Although a morphological continuum may be evident from the histological evaluation of preneoplastic and neoplastic lesions, it is not axiomatic that all preneoplastic or benign lesions progress. The probability of regression or progression from one category to another, or the rates at which these might occur, are seldom known for spontaneous or induced neoplasms. Host factors as well as exogenous stimuli may influence these events. The concept of neoplastic progression and the limitations of our knowledge of the biological behavior of preneoplastic lesions and benign neoplasms are important considerations in the interpretation of pathology data from carcinogenicity studies.