HER2 Copy Number in the Assessment of HER2 Status in Gastric/GOJ Cancers: Does It Matter?
Priyanthi Kumarasinghe, Bastiaan de Boer, Khor Sheng, Esther Ooi, Sureshika Jayasinghe, Stephen Fox. PathWest, QEII Medical Centre, Perth, WA, Australia; Massachusetts General Hospital, Boston, MA; Peter MacCallum Cancer Centre, St Andrews Place, Melbourne, VIC, Australia; University of Western Australia, Perth, WA, Australia
Background: Following the results of the ToGA study, combination chemotherapy with trastuzumab was approved to treat HER2 positive advanced/metastatic gastric & GOJ carcinomas. HER2 positivity was defined as either an IHC 3+ score or HER2 amplification as determined by HER2/Chr17 ratio ≥2.0 rather than the HER2 copy number (CN) per cell. Sub group analysis showed that there was no survival benefit for the HER2 amplified but IHC negative group (score 0 or 1+) which was ∼ 23% of the positive cohort. We aim to compare HER2 CN against HER2/Chr17 ratio in relation to the IHC score.
Design: HER2 status of gastric and GOJ cancers were assessed by IHC and silver in-situ hybridisation (SISH). IHC scoring (0-3+) was performed using "modified gastric" criteria. HER2 and Chr17 CNs were counted in at least in 20 cancer cells and the HER2:Chr17 ratio calculated as per protocol. These were compared to the IHC scores.
Results: There were 142 gastric & GOJ carcinomas.
|IHC Score (No: of cases)||Mean CN||Range||Mean ratio||Range|