In vitro thymidine labelling of human pulmonary neoplasms.

The in vitro thymidine labelling indices (TLI) of 58 human lung tumours were assessed using autoradiography. The labelling technique involved incubation of 1 mm3 tumour fragments with 3H-thymidine (5 muCi ml-1) under conditions of hyperbaric oxygenation at a pressure of 3 atmospheres. Only a rim of labelling was achieved along the edges of fragments and the depth of this rim varied from tumour to tumour. A technique for counting TLIs was therefore devised to take this into account. In general, those tumours showing low TLI values of less than 5.0% showed a greater depth of labelling. The common malignant tumours of the bronchus showed a wide range of values (2.2-30.4%) though the adenocarcinomata had a lower average value than the other groups. With the squamous carcinomata a relationship with differentiation was shown. The mean value for small cell carcinomata (16.9%)--a highly aggressive tumour--was no higher than for the other groups. The low grade malignant tumours showed TLIs of less than 3.0% and these values correlate with their less aggressive clinical behaviour. Labelling of stromal cells and inflammatory cells varied greatly from tumour to tumour; however, no correlation was found with the TLIs of tumour cells.