Tumor-Infiltrating Lymphocytes in Breast Cancer

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Data have shown that tumor-infiltrating lymphocytes (TILs) can be used to predict response to anthracycline-based chemotherapy regimens in triple-negative breast cancer (TNBC) after neoadjuvant chemotherapy, says Carlos L. Arteaga, MD. Additionally, next-generation sequencing has demonstrated an association between the level of TILs and genomic alterations in the RAS/MAP kinase pathway. This suggests that mitogen-activated kinase (MEK) inhibitors might synergize with immunotherapies in TNBC with alterations in the RAS pathway, Arteaga postulates.

In addition to the setting of TNBC, research has determined that the presence of TILs is prognostic overall in the HER2-positive setting as well, says Edith A. Perez, MD. Approximately 10% of individuals with HER2-positive breast cancer have high levels of TILs in the stroma (defined as more than 60%). This may be associated with additional benefits with trastuzumab, as well as with chemotherapy, in this subset of patients.

The relationship between the benefit achieved from immune checkpoint blockades and the percentage of TILs has not been reported yet, says Perez. A better understanding of how to stimulate TILs and condition them to be more sensitive to immunotherapy is needed, comments Debu Tripathy, MD. However, at this point the level of TILs should not be regularly obtained, suggests Denise A. Yardley, MD, stating that it is currently not actionable information.