Sergio Laurito¹, María Teresita Branham¹, Emanuel Campoy¹, Sebastián Real¹, Juan Cueto¹, Francisco Gago², Telma Glatstein³, Paola De la Iglesia4, María Roqué¹
HER2 overexpressing tumors represent 15-20% of invasive ductal breast carcinomas (IDC). Even though they are treated with the monoclonal antibody trastuzumab, 20% of primary and 70% of metastatic HER2 tumors develop resistance. HER2 belongs to a 4-member oncogene family (HER1-4), which present the capacity to compensate inhibition. We believe it is relevant to know the state of the whole family to predict response to treatment. Here we have designed a probe mix to detect the amplification of the 4 HER oncogenes. One hundred and eleven IDC (54 fresh frozen and 57 FFPE) were analyzed byMLPA, and HER2 determination was validated prospectively by FISH, IHC and CISH (Pearson r=0.95; 0.59; 0.97 respectively, p<0.0001). Positive correlation between CNV and expression was observed in wet and in-silico analyses for the 4 oncogenes (Spearman Rank test p<0.05). Of the 111 included samples, 26.12% presented at least one HER amplified, of which 23.07% showed co-amplifications. In addition, we developed a protocol based on MLPA-ddPCR, which allows the detection of the tumor proportion of co-amplified HER. In this case, MLPA reactions were performed on single cells using Taqman probes, and then analyzed by ddPCR. By this, we detected intra-tumor heterogeneity for HER co-amplifications. Here we present 2 tools based in MLPA that can identify the co-amplification level and the intra tumor heterogeneity of the 4 HER oncogenes, contributing to the precision medicine of breast cancer patients.