There are three categories of cytostructural changes which can be used as criteria for malignancy. These include (1) nuclear changes-in¬ creased nuclear/cytoplasmic ratio, hyperchromasia, irregular clumping of chromatin, increase in num¬ ber and size of nucleoli, tabulation and nuclear gigantism, and overlapping; (2) cytoplasmic changes-excessive vacuolization and leukocyte in¬ clusions; and (3) criteria from groups-clumping, indistinct borders, and increased size. Of these, the nuclear changes are most definitive, particular¬ ly clumping and irregular distribution of chromatin. These criteria alone are present with cytologi-