HER2 testing in gastric adenocarcinoma
Session type: Poster / e-Poster / Silent Theatre session
Theme: Diagnosis and therapy
Patients with HER2 positive metastatic gastric adenocarcioma have been shown to benefit from trastuzumab (Herceptin) therapy. NICE guidance recommends initial determination of HER2 status by immunohistochemistry (IHC) with scores ranging from 0 to 3+ (0 and 1+ are negative, 2+ is equivocal and 3+ is positive). Fluorescence in situ hybridisation (FISH) for HER2 amplification is reserved for equivocal 2+ cases. Only those patients with tumours scored 3+ on IHC or 2+ on IHC followed by a positive FISH result are eligible for trastuzumab treatment.
This is a retrospective study of cases of gastric adenocarcinoma tested for HER2 at the Queen Elizabeth Hospital Birmingham between 2013 and 2015. Both in house and external referral cases are included. The Hercept-test antibody supplied by Dako is used for IHC and the PathVysion Kit II supplied by Abbott Molecular is used for FISH.
A total of 338 cases of gastric adenocarcinoma were successfully tested. The majority (61%) of cases were negative by IHC. There were 79 cases (23%) with 2+ IHC scores that were tested for FISH, of which 49% were found to be FISH positive. The overall number of HER2 positive results (3+ IHC cases and 2+ IHC FISH positive cases) was 93 (28%).
The overall rate of 28% HER2 positivity was slightly higher than the rate of 15-20% quoted in the literature. This may be because this data comprises a mixture of in house and referral cases. The finding that almost half of tumours with a 2+ IHC score were FISH positive is reassuring, and justifies the current practice of using FISH in equivocal cases.