Targeting ERBB2 mutations in solid tumors: biological and clinical implications.

Preclinical data have shown that ERBB2 activating mutations are responsive to HER2 tyrosine kinase inhibitors. The aim of this study is to characterize the landscape of ERBB2 mutations in solid tumors and the potential efficacy of ERBB2 targeting.We analyzed the next-generation sequencing results from 17,878 patients with solid tumors and reported the outcome of 4 patients with advanced ERBB2-mutated tumors treated with a combination of trastuzumab and lapatinib.ERBB2 mutations occurred in 510 patients (2.85%). The tumor types with the highest incidence of ERBB2 mutations were the following: bladder (16.6%), small bowel (8.6%), ampullar (6.5%), skin non-melanoma (6.1%), and cervical cancer (5.5%). 49.4% (n = 282) were known as activating mutations. ERBB2 mutation was not mutually exclusive of ERBB2 amplification which occurred in up to 10% of cases. PI3KCA activating mutations were associated with ERBB2 mutations in 12.4% of cases mainly in breast and lung cancer. Four patients (endometrial, colorectal, cholangiocarcinoma, and adenosarcoma of the uterus) were treated with a combination of trastuzumab and lapatinib. All of them experienced tumor shrinkage resulting in stable disease in three cases and partial response in one case. One patient developed secondary resistance. Sequencing of the progressing metastasis allowed the identification of the ERBB2 L869R mutation previously associated with resistance to lapatinib in vitro.These results support further clinical investigation aiming to demonstrate that ERBB2-mutational driven therapy can improve patient care irrespective of histology.