High concordance rate of HER2 status assessed via silver in situ hybridisation (SISH) between core biopsy and excision specimens: a 4 year retrospective review from a single institution

HER2 genomic heterogeneity is a frequent event in gastroesophageal adenocarcinoma and correlates with tumor morphology

AIM

To characterize a cohort of gastro-esophageal adenocarcinomas (GEA) evaluated for HER2 gene amplification using bright field in situ hybridization (ISH) following the 2016 guidelines for GEA and correlating the results with clinico-pathological features. It was also aimed to evaluate the effect of applying the ISH criteria from the 2018 guidelines for breast cancer (BC) in the same GEA cases.

MATERIALS AND METHODS

159 GEA cases collected in a period of 59 months were evaluated for HER2 gene amplification by ISH according to GEA and BC guidelines. All cases were reviewed for histological type, grading and presence of signet ring cells.

RESULTS

Most of the cases refereed to ISH were HER2 equivocal (57.9 %) by immunohistochemistry. According to the GEA guideline, 131 cases were HER2-negative (87.3 %) and 19 cases were HER2-positive (12.7 %). According to the BC guideline, 133 cases were HER2-negative (88.7 %) and 17 cases were HER2-positive (11.3 %), being statistically similar to the results obtained with the GEA guideline. HER2 genomic heterogeneity was detected in 31.6 % of the HER2-positive cases, almost exclusively in tubular adenocarcinoma. We observed a significant association between HER2 gene amplification and tubular adenocarcinomas, and absence of signet ring cells. The only case with HER2 gene amplification and presence of signet ring cells was a mixed carcinoma, where the signet ring cells represented the non-amplified component.

CONCLUSIONS

HER2 positivity rate was similar when applying the GEA or the BC guidelines. We also establish a tight association between morphology and HER2 gene amplification.

Predicting discordant HER2 results in ipsilateral synchronous invasive breast carcinomas: experience from a single institution

With the emergence of multiple lines of highly effective Human Epidermal Growth Factor Receptor 2 (HER2) directed therapy, accurate identification of HER2 positive tumour has become a critical aspect in the histopathological analysis of breast cancers. Multifocal invasive breast carcinomas are relatively common, and given the aggressive inherent biology of HER2 positive disease, identification of even small tumours with HER2 positive status may be of importance for treatment planning. There are currently no clear guidelines as to whether all of these foci should be tested for HER2 status. We reviewed the results of 172 patients in whom HER2 in situ hybridisation (ISH) testing was performed on at least two ipsilateral synchronous invasive carcinomas. Discordant results in different invasive foci were relatively uncommon and occurred in only eight (5%) of the 172 patients. This showed a statistically significant correlation with similarly discordant oestrogen receptor (ER) results. In addition HER2 discordance was more likely amongst different tumour foci if these arose in distinct and separate areas of DCIS. An algorithm based on a combination of College of American Pathologists (CAP) recommendation for HER2 testing, differing ER status and background DCIS profile may be useful in detecting these discordant cases.