This classification is based primarily on the microscopic charac teristics of tumours and, therefore, is concerned with morpho logically identifiable cell types and histological patterns, as seen with conventional light microscopy. The term tumours is used synonymously with neoplasm. The phrase tumour-like is applied to lesions which resemble neo plasms, clinically or morphologically, but do not behave biologi cally in a neoplastic manner. They are included in this classifica tion because they give rise to problems in differential diagnosis and because of the unclear borderline between...