TILs: A Decade of Research Shapes Global Standards for Breast Cancer

Roberto Salgado, MD, anatomic pathologist for breast cancer translational research at Institut Jules Bordet in Antwerp, Belgium, discusses TILs among triple-negative, HER2-positive, and HR-positive breast cancer subtypes. He highlights the standardized method for TIL assessment developed a decade ago that has been adopted globally. The standardized method has improved the accuracy and consistency of TIL assessments, leading to better prognostication and potential treatment decisions.

Salgado presented an update on the 10 years worth of research of TILs at the San Antonio Breast Cancer Symposium 2024 between December 10 to December 13.

This transcript was lightly edited for clarity.

Transcript

How do TILs differ across various subtypes of breast cancer?

There are indeed specific subtypes of breast cancer, which is based mainly on whether the hormone receptors are positive or not, and whether there is an additional molecule present or not, which is called HER2.

We have a subtype which is called triple negative breast cancer, so triple negative, so three times negative, which is a tumor that is negative for the hormone receptors, estrogen and progesterone receptors, and also for HER2. Most of the information that we already have on TILS is based on that tumor type.

The second most prevalent tumor type concerning the extent of the immune system is HER2 positive disease. There, we also have a mountain of evidence that the immune system is able to predict whether the cancer will come back in the patient or not, and that's useful information for the clinician to know. We are not that far in our knowledge on how this information may be used by clinicians.

In triple negative breast cancer, we start to understand how clinicians may potentially use this information to determine treatment options. In HER2 positive disease, we know it's prognostic. We know that the clinician cannot determine the risk of recurrence of that cancer in a particular patient without knowing the immune system but how we should act therapeutically, that's something that we still need to decipher.

The third subtype is the hormone receptor positive subtype of breast cancer, which is not triple negative and not HER2 positive. That's a subtype where we start to understand the importance of the immune system. Probably in 2025, we will have a new set of data that will help us decipher the importance of the immune system in that particular subtype.

How has the assessment of TILs evolved over the past decade?

Well, the advantages is that we developed 10 years ago with the TILs working group, this International Immuno-Oncology Biomarker Working Group, a method which is still standing 10 years later.

I think we can safely say that there is no analysis of TILs worldwide that is not using the method that the working group has developed. I think this is a very strong message. We have developed an easy to understand method, an easy to incorporate method.

This has helped us to develop studies globally. We just finalized a study and published it in JAMA, Journal of the American Medical Association, a few months ago, where we took a data set from Japan, from South Korea, from many countries in Europe and the United States, where we have analyzed the TILs with exactly the same method. We are able to pull together thousands of patients in one single analysis.

The fact that we have not changed the method drastically, or not at all, is a very powerful message for helping to get this biomarker into daily practice.