Lin SY, Wang YH, Hsu CY, et al. - HER2 immunohistochemistry (IHC) was evaluated in ovarian clear cell carcinoma (OCCC) employing two antibodies and two scoring guidelines in association with HER2 amplification and clinicopathological features. Researchers generated tissue microarray using a total of 71 OCCC cases for IHC (A0485 and 4B5) and dual-color silver in-situ hybridization (DISH). The IHC was independently scored by two pathologists using the 2018 ASCO/CAP breast cancer guidelines (breast guidelines) and the 2016 ASCO/CAP gastro-oesophageal adenocarcinoma guidelines (gastric guidelines). Between A0485 and 4B5, IHC concordances were 87.3%-93.0%. HER2 amplification was established in 7% of OCCC cases and there was significant association of the molecular change with papillary-predominant growth patterns. Combined 4B5 IHC with gastric guidelines presents the best sensitivity in predicting HER2 amplification, and fewer equivocal (IHC 2+) cases. In view of the observed intratumoural heterogeneity, they emphasize assessing HER2 status on whole tissue sections and on both primary and metastatic tumour specimens.