Outcome of HER2 Testing by FISH applying ASCO/CAP 2007 and 2013 guideline in IHC equivocal group of breast cancer: Experience at tertiary cancer care centre.

BACKGROUND AND OBJECTIVES: HER2 testing guideline of ASCO/CAP for interpretation and reporting has recently been revised. The study is aimed to measure the impact of 2013 CAP guideline on equivocal HER2 test outcome (immunohistochemistry [IHC] 2+) when tested by fluorescent in situ hybridization (FISH). The study also aims at finding the frequency of polysomy and monosomy of chromosome 17.

MATERIALS AND METHODS: Specimens were collected in Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, India. IHC was performed in every case, and FISH was performed in IHC2+ cases.

RESULTS: In final analysis includes 557 subjects on the basis of CAP guideline 2007 and CAP guideline 2013. One hundred ninety-two subjects (34.4%) were HER2 amplified according to CAP scoring 2007, and 246 subjects (44%) according to 2013 CAP scoring.

CONCLUSIONS: FISH results were evaluated (IHC2 + interpreted according to CAP 2007 guideline) with both 2007 and 2013 ASCO/CAP scoring criteria, we identified significantly more HER2 positive cases as compared to cases evaluated using the 2007 criteria ( P < 0.05). We also found that in breast carcinoma, HER2 status in the presence of polysomy 17 may vary with the scoring criteria used. Evaluation of FISH result using 2013 ASCO/CAP criteria means that more patients with breast cancer may be appropriate for targeted treatment with trastuzumab, potentially improving their outcome.