I would like to talk about this, as time and again, I have been seeing people treated elsewhere, where they have received Herceptin for some time (where HER2 was 3+ on IHC), and then suddenly the FISH report comes negative.
For making it concise, I am not going to explain what is IHC and what is FISH and other details. You can google it up. I will stick to the point.
1. When is FISH done?
FISH is done for tumours which test '2+' on HER2 testing on IHC. HER2 has three possibilities o IHC:
1+ means negative
2+ means equivocal (could be negative or positive)
3+ means positive and will benefit from Herceptin.
So when on IHC, it is 2+, we are not very sure it is positive or negative and hence we do a confirmatory test - FISH
Remember, IHC is a pathologist dependent test. One pathologist may report it as 2+ and other pathologist may report it as 3+. A pathologist who is experienced in IHC and cancer reporting, is much less likely to make an error.
2. So when is Herceptin given?
Herceptin is given for those who are HER2 3+
3. Is IHC 3+ enough to give Herceptin? or is FISH mandatory for even IHC 3+ tumours?
According to worldwide guidelines, Herceptin can be given for IHC 3+ tumours, and FISH is not needed.
However, mark my words, the IHC has to be done by standardised labs and 'experienced' pathologists. This is where India faces a problem. If a substandard lab reports IHC as 3+ (which could be negative as well), we are risking a patient's life by giving Herceptin, as Herceptin, though beneficial from cancer point of view, can cause damage to heart.
It's extremely important here to stick to standard labs.
There are many so called 'standard' labs all over India, where only the name is standard, the pathologists keep on changing every few years. You see, its very very difficult to accept a IHC report from there. Even in a large city like Mumbai, there are barely 5 to 10 labs whom we can genuinely rely on IHC reports.
Hence, my team follows the following principle:
For IHC HER2 1+, no further testing.
FOR IHC HER2 2+, FISH is surely done.
FOR IHC HER2 3+, for most cases, we still do a FISH testing to confirm the positivity, unless the report is from Tata Memorial Centre or a few other places (Tata and some of these Hospitals have the best possible pathology reporting). The idea is, anyways, by giving Herceptin, the patient is going to spend more than 3 to 4 lakhs, apart from consequences of Herceptin on heart. FISH testing does not cost more than 15000 in standard places, and here, in some cases, we even get it free of charge. And the report does not take more than 7 days. So we wait, ensure that FISH is positive an only then give Herceptin.
And please note, this is the methodology of only my team. It is not a standard at all, and other oncologists may not agree to it, which is fairly fine enough.