Case 1: When to Use FISH Testing in Breast Cancer

Ian Krop, MD, PhD: There was a time not long ago when there seemed to be discussion regarding the potential for false-negative IHC [immunohistochemistry] tests and the push to try to do the FISH [fluorescence in situ hybridization] test as the initial test to avoid false-negatives. My institution does the same thing that yours does. We do an IHC test on all patients and then do a FISH assessment only for equivocal cases. Did that point about doing upfront FISH testing kind of die out? Are there data about that? What do you think?

Evita Sadimin, MD: We actually did that at our institution for a certain period of time. We did FISH first, upfront, for everything, whatever the case. This was before the updated 2018 [American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP)] guidelines. So we were doing FISH first, and a significant number of cases fell into equivocal criteria. Now, with the most current 2018 [ASCO/CAP] guidelines, there is no equivocal criteria anymore, so it becomes more difficult if you start FISH first, at least for practical purposes in our institution.

Adam Brufsky, MD, PhD: It sounds like it’s a resource issue. Is it harder to do FISH than IHC, for your staff and everybody else?

Evita Sadimin, MD: We did that for about 3 years. We were OK resource-wise doing FISH first, but it just became impractical to do with the 2018 criteria.

Adam Brufsky, MD, PhD: You’d have to recount everything, and there were different nuclei and stuff. Is that why, with the new guideline?

Evita Sadimin, MD: We lost the equivocal criteria in 2018.

Hope Rugo, MD, FASCO: I think that was a big improvement, right? I think it’s a really fascinating area of discussion, and I think the new guidelines have been a huge improvement in not treating a whole lot of people who probably didn't have HER2-positive disease with that equivocal group. I think we’ve made some nice progress.

Transcript edited for clarity.