ASCO/CAP guidelines on breast tissue fixation; standardization? really?

After multiple events of patient samples not being managed in an optimal fashion, guidelines were published in 2020 and updated in 2023 regarding fixation of breast tissue samples tested for ER/PR/Her2 expression. 

“Samples for ER and PgR testing are fixed in 10% NBF for 6 to 72 hours”

We all agree that this was welcome, to try and standardize the tissue handling. And the recommendation was qualified as “strong” which convinced many laboratories to abandon some locally developed algorithms to match these recommendations.

But how normalized are we really now? One obvious question is NBF’s composition. What is the standard recipe that all manufacturers must adhere to?

Well, it appears that there is simply no such thing as a standard NBF recipe. The reference publication (1) I am personally referring to states: 3,7% of formaldehyde, and respectively 0,35 and 0,65 % w/v of monosodium and disodium phosphate. 

It is very interesting to then compare this recipe to the SDS data sheets of the various US suppliers of NBF. In these, formaldehyde content varies from 3.5-4.0%,  4%, less than 4%, less than 6% and “trade secret”! Methanol content swings from less than 1%, through 1-1.5% all the way to less than 2%. If the buffer salts are usually similar, sometimes they are completely replaced by their components of phosphoric Acid and sodium hydroxide. 

A 10% NBF solution should be 3.7%, since formaldehyde saturates at 37%, and not all products offer this.

We, at Chaptec, have developed our own recipe of NBF that we call TissuFix®. It is a formaldehyde based; phosphate buffered fixative which qualifies it as an NBF. The concentrations of the components are, just like others, unique to our own recipe. (6% formaldehyde and 1.5-2% methanol) And if you ask around, you will find a lot of laboratories that will tell you that, especially for fatty tissue, this solution fixes faster, much faster than any other NBF.

It seems to me that the whole objective of the guidelines in the beginning was that all breast samples were adequately fixed right?  That objective seems close now, despite the lack of standardization of the reagent itself. Which leads us to propose that TissuFix® is a perfectly acceptable NBF formulation for breast tissue fixation that follows the guidelines, and probably a more efficient one, in this very unstandardized world! Now, why don’t you find out by yourself and ask for a sample?

1. Why were guidelines published regarding the fixation of breast tissues for ER/PR/Her2 testing?

Because many samples were not being properly fixed, which compromised the reliability of test results. The guidelines were therefore created to standardize fixation practices.

2. What do these guidelines recommend?

That samples intended for ER and PgR testing be fixed in 10% neutral buffered formalin (NBF) for 6 to 72 hours.

3. Did this recommendation have a real impact in laboratories?

Yes. The recommendation was designated as “strong,” which prompted many laboratories to abandon their local protocols and adopt these standardized guidelines.

4. Is there a standardized recipe for 10% NBF?

No. Despite its widespread use, there is no single formulation that all manufacturers follow.

5. What NBF formulation does Chaptec offer?

Chaptec provides TissuFix®, an NBF characterized by:
• 6% formaldehyde
• 1.5–2% methanol
• A phosphate buffer

6. What advantages have been observed with TissuFix®?

According to several laboratories:
• Faster fixation, especially in fatty tissue
• Comparable or superior results to other NBF formulations
• Reliable reproducibility for ER/PR/Her2 testing

7. If formulations differ, is the goal of the guidelines still achieved?

Yes. Despite the lack of complete standardization, the main objective—adequate fixation of breast tissue—appears to be successfully achieved in most cases, including with TissuFix®.

8. How can I implement breast tissue fixation guidelines in my laboratory?

Since multiple NBF formulations are used successfully, TissuFix® is a fully acceptable and effective alternative, and is worth evaluating in laboratory practice.