Evidence is growing to support the idea that the immune system plays a role in some breast cancers and that tumour infiltrating lymphocytes (TILs) can predict prognosis and response to therapy.

Given TILs can be easily estimated on hematoxylin and eosin stains, they offer a relatively simple biomarker that can potentially help direct therapy.

According to a review article on TILs in breast cancer, there is a strong linear relationship between increased levels of TILs and disease free survival in triple negative and HER2-positive disease.

Co-author Associate Professor Sherene Loi, from the Peter MacCallum Cancer Centre, told the limbic the heterogeneity within breast cancer had largely hidden the immune signal in some breast cancer subtypes.

“People always think the immune system is involved in every cancer but certainly for breast cancer, it was traditionally thought the main risk factors were reproductive and genetic.”

“Once we realised that breast cancer was three different diseases and starting looking more into what drives prognosis in breast cancer subtypes, we identified the immune signal is much stronger in triple negative and HER2-positive breast cancer.”

“So patients who have more TILs do better…but we don’t know why some women have better immune systems or can generate a better immune response to their breast cancer.”

Associate Professor Loi said TILs will be a marker for immune therapies such as pembrolizumab (Keytruda) or nivolumab (Opdivo), which were already approved for melanoma.

“They’ve only just been evaluated in breast cancer…but for patients who do get a response, the response is very durable for patients with advanced disease and they have an excellent quality of life.”

She said TILs will also help identify which women might need more or less therapy – either adding extra therapies onto checkpoint blockade or giving less chemotherapy in combination with trastuzumab.

Results from the IMpassion 130 trial, evaluating atezolizumab in combination with chemotherapy as a first line treatment for newly diagnosed advanced triple negative breast cancer, were due in mid-late 2018.

“If it’s positive, then I think there will be a change in the standard of care at that point,” Associate Professor Loi said.