Labelling of consecutive sections with antibodies against IGF-I and proliferating cell nuclear antigen (PCNA)/cyclin demonstrated a co-distribution of the 2 antigens in carcinoid tumours.
Mean PCNA expression was higher in squamous carcinomas than in adenocarcinomas but there was marked intra-tumour variation in PCNA index in almost all cases.
Heterogeneity of expression of the proliferating cell nuclear antigen (PCNA) was assessed immunohistochemically in 156 tissue samples from 33 surgically resected pulmonary carcinomas using the monoclonal antibody 19A2.
The wide variation in PCNA expression between different samples within a tumour would indicate that systematic sampling and counting will be necessary in future immunohistochemical studies of cell proliferation in tumour material.