This classification is based primarily on the microscopic characteris tics of tumours and therefore is concerned with morphologically identifiable cell types and histological patterns as seen with conven tional light microscopy. The term tumour is used synonymously with neoplasm. The phrase tumour-like is applied to lesions that clinically or morpholog ically resemble neoplasms but do not behave biologically in a neo plastic manner. They are included in this publication because they give rise to problems in differential diagnosis and because of the un clear distinction between neoplasms and...