Aims: To validate the use of the silver-enhanced in situ hybridization (SISH) technique in assessing HER2 status of breast carcinoma in excision biopsy specimens, and to assess its reliability in determining HER2 status in core biopsy specimens.
Methods and results: Routinely processed paraffin sections of 65 excised breast carcinomas and 56 available preoperative core biopsy specimens from the same patients were selected from the archives for testing with the SISH technique using the automated Ventana Benchmark XT machine. For each case, two sections were used, one for the assessment of HER2 gene amplification and the other for assessment of chromosome 17. Of the 65 excision specimens tested, sections of 53 cases were also available for fluorescence in situ hybridization (FISH) examination. HER2 gene amplification was detected by SISH in 14 (21%) out of 65 excision specimens and in eight (14%) out of 56 core biopsy specimens. The results of SISH and FISH were identical in 50 (94%) out of the 53 excision cases examined by the two techniques. Two cases were SISH-, FISH+, and one case was the other way round. SISH results of core biopsy specimens and corresponding excision biopsy specimens were identical in 50 (89%) out of 56 cases. Four cases (7%) were SISH- in cores but positive in excision specimens, whereas two cases were the other way round.
Conclusions: The results validate the use of the SISH technique for assessing HER2 status of excised breast carcinoma tissue sections. The results are comparable to those obtained with FISH, but SISH has the advantage of having a permanent end result that can be visualized by an ordinary light microscope. There is a reasonable 89% concordance between SISH results obtained in core and excision biopsy specimens. However, it may be prudent to postpone doing SISH, if possible, until sections of the resected specimen are available, as these seem to be more reliable.