Aims Advanced gallbladder carcinoma (AGBC) carries a poor prognosis with dismal survival. There are no data regarding HER2/ERBB2 expression in AGBC. This study evaluated the overexpression of HER2/ERBB2 in cytological aspirates from AGBCs to identify potential patients for whom anti-HER2 targeted therapies can benefit.

Methods This prospective, case–control study was performed on 50 primary AGBC cases. A detailed cytomorphological assessment, followed by immunocytochemistry (ICC) for HER2/ERBB2, was performed on AGBC cell blocks. A similar number of age-matched and gender-matched resected chronic cholecystitis specimens were included as controls. Fluorescence in situ hybridisation (FISH) was performed in equivocal cases.

Results A total of 10 (20%) cases showed positive (3+), 19 (38%) equivocal (2+) expression and 21 (42%) were negative on HER2/ERBB2 ICC. None of the equivocal cases demonstrated HER2 amplification by FISH. Among the controls, none showed positive (3+) immunoexpression, 23 (46%) demonstrated equivocal expression and 27 (54%) were negative. On statistical analysis, HER2/ERBB2 overexpression was significantly associated with AGBC compared with the controls. Of all the clinical, radiological and cytomorphological parameters, the predominant papillary or acinar arrangements of the tumour cells were significantly associated with HER2/ERBB2 overexpression.

Conclusions This is the first study to evaluate the expression of HER2/ERBB2 on cytological aspirates in AGBC using ICC and FISH. HER2/ERBB2 overexpression(20%) was significantly associated with AGBC. Furthermore, predominant papillary or acinar arrangements of tumour cells in the cytological smears were significantly associated with HER2/ERBB2 overexpression. They can serve as potential predictors of HER2/ERBB2 overexpression to select AGBC patients for anti-HER2 targeted therapies.