On TILt.

July 31, 2017. You may hear someone ask if there are tumor infiltrating lymphocytes (TILs) present in a tumor specimen. And while the answer may offer some prognostic value, will it really change what you do? An interesting secondary analysis in JAMA Onc this week looks at whether the presence of TILs (specifically CD8+ cytotoxic T cells) influences response to different types of HER2-targeted agents. The key to this study is understanding that HER2-signaling can be targeted either by monoclonoal antibodies (trastuzumab) that bind the HER2 receptor or by small molecules (lapatinib) that enter the cell and inhibit the tyrosine kinase component. The original data is from the MA.31 trial, which determined that trastuzumab offers superior progression free survival compared to lapatinib. Interestingly, tumors with low TILs responded even worse to lapatinib (small molecule inhibitor) than those with more TILs. So we now know that presence of TILs is not only prognostic, but it is also predictive...and you really should know the difference.