Method for grading breast cancer.

labelling.' PCNA immunohistochemical expression (evaluated with the PCI0 mono- clonal antibody) seems to be related to cellular proliferation in many normal tissues and in some neoplasms,2 such as gastro- intestinal lymphomas,3 central nervous sys- tem tumours,4 lung neuroendocrine neoplasms,' and prostatic carcinomas.'However, in other tumours, like breast and gastric cancer, PCNA (PC 10) expression seems aberrant and not strictly related to proliferative activity.' 7 8 Various factors unrelated to cell proliferation may influence the immunohistochemical expression of PCNA, including posttranscriptional regulation (and deregulation) of the PCNA gene,8" long half-life of the PCNA protein,'0 involvement of PCNA pro- tein in DNA repair synthesis," and tissue and section processing-type and ionic strength of the fixatives, fixation time, section heating, immunohistochemical techni-