Comparison of BrdU and cyclin A as markers of the S-phase in oval precancerous lesions

A study comparing bromodeoxyuridine (BrdU) and cyclin A as markers of cells in the S-phase in oral precancerous lesions was performed. These were also compared with the growth fraction (GF) as assessed by Ki-67. Biopsies of 15 lesions were obtained, presenting clinically as leuhoplakia or erythroplakia of the lateral tongue or floor of mouth. Half of each biopsy was incubated in BrdU and routinely fixed and processed. Sequential sections from each block were cut and stained immunohistochemically with antibodies against the following proteins: BrdU, Ki-67 and cyclin A. Stained sections were quantified and the labelling indices (LI) expressed per 100 of the total nucleated cell population (%) and per millimetre basement length (/mm). The mean LI% for BrdU was 11.24% (SD 2.83), for cyclin A it was 12.76% (SD 3.88) and the GF% was 29.25% (SD 11.88). The mean Ll/mm for BrdU was 40.93/mm (SD 11.88), for cyclin A it was 47.59/mm (SD 18.28) and the GF/mm was 110.72/mm (SD 49.30). The BrdU and cyclin A indices were significantly correlated with each other. In the more dysplastic cases, the cyclin A LI was quantitatively much larger than that for BrdU, suggesting that the protein was being overexpressed. It was concluded that as a tool to study the kinetic aspects of the cell cycle in dysplastic lesions cyclin A was limited by the fact that it is overexpressed. In minimally dysplastic lesions and normal epithelia, however, cyclin A may be a viable alternative to BrdU for the study of the S-phase.