Expression of bcr–abl mRNA in individual chronic myelogenous leukaemia cells as determined by in situ amplification

We present the results of a novel method developed for evaluation of in situ amplification, a molecular genetic method at the cellular level. Reverse transcription polymerase chain reaction (RT‐PCR) was used to study bcr–abl transcript levels in individual cells from patients with chronic myelogenous leukaemia (CML). After hybridizing a fluorochrome‐labelled probe to the cell‐bound RT‐PCR product, bcr–abl mRNA‐positive cells were determined using image analysis. A dilution series of bcr–abl‐positive BV173 into normal cells showed a good correlation between expected and actual values. In 25 CML samples, the percentage of in situ PCR‐positive cells showed an excellent correlation with cytogenetic results (r = 0·94, P