Detection of Gene Amplification by Multiplex Ligation- Dependent Probe Amplification in Comparison with In Situ Hybridization and Immunohistochemistry

Gene amplification is an important mechanism in the development and progression of cancer. Currently, gene amplification status is generally determined by in situ hybridization (ISH). Multiplex ligation-dependent probe amplification (MLPA) is a PCR-based method that allows copy number detection of up to 50 nucleic acid sequences in one reaction. The aim of the present study was to compare results for HER2, CCND1, MYC and ESR1 gene amplification detected by MLPA with fluorescent in situ hybridization (FISH) and chromogenic in situ hybridization (CISH) as clinically approved methods. Tissue samples of 170 invasive breast cancers were collected. All were ER positive. Tissue samples had previously been tested for HER2 using immunohistochemistry. Amplification of the selected genes were assessed using MLPA, FISH and CISH and results were compared. HER2 MLPA and ISH results were also compared with HER2 immunohistochemistry (IHC) which detects protein overexpression. Amplification of HER2, CCND1, MYC and ESR1 by MLPA were found in 9%, 19%, 20% and 2% of samples, respectively. Amplification of HER2, CCND1, MYC and ESR1 by FISH was noted in 7%, 16%, 16% and 1% of samples, respectively. A high level of concordance was found between MLPA/ FISH (HER2: 88%, CCND1: 88%, MYC: 86%, ESR1: 92%) and MLPA/ CISH (HER2: 84%). Of all IHC 3+ cases, 91% were amplified by MLPA. In IHC 2+ group, 31% were MLPA amplified. In IHC 1+ group, 2% were MLPA amplified. None of the IHC 0 cases were amplified by MLPA. Our results indicate that there is a good correlation between MLPA, IHC and ISH results. Therefore, MLPA can serve as an alternative to ISH for detection of gene amplification.