In situ localization of S-phase-specific histone (H3) mRNA in Bowen's disease

PCNA and Ki-67 immunohistochemistry has been used to assess cell proliferat ion in place of tritiated thymidine or BrdU labeling of S-phase cells. Rece ntly, it has been possible to reliably demonstrate histone H3 mRNA by in si tu hybridization in formalin-fixed and paraffin-embedded tissue sections. We have compared this new proliferation marker with Ki-67 and PCNA with reg ard to distribution of positive cells and labeling indices (LI%) for 22 cas es of Bowen's disease. In normal skin, Ki-67-IHC positive cells and histone mRNA positive cells were observed in the basal and suprabasal layers of th e epidermis. In Bowen's disease, positive cells with each marker were more frequent in upper neoplastic epidermis than in suprabasal layers, and the a verage LI%s were markedly elevated with all markers, the scores decreasing in the following order: PCNA-IHC, Ki-67-IHC and H3mRNA-ISH. However, the re sults of double staining demonstrated that S-phase cells do not necessarily show exactly the same distributions as with PCNA and Ki-67-IHC labeling. H 3mRNA-ISH showed three different degrees of reaction with significantly dif ferent LI%s, whereas PCNA and Ki-67 LI% did not vary essentially in the sam e areas. These results strongly suggest that Bowen's disease, which is well known as a low-grade neoplastic state with malignant potential, also demon strates clear intratumoral heterogeneity of S-phase cells using the H3mRNA- ISH method.