TIL death do us part.

There is mounting evidence that tumor-infiltrating lymphocytes (TIL) play a--albeit poorly understood--role in breast cancer outcomes. The newest study in Lancet Oncology evaluated TILs in core biopsy specimens from >3K patients across six German Breast Cancer Group trials. They found, like others before them, the extent of TILs was associated with response to chemo. But let’s back up for a minute: It’s important to understand how they actually measured TILs, which as it turns out were counted in the stroma of the tumor specimen rather than in actual tumor nests. They then estimated the percentage of all stromal immune cells present that were mononuclear (i.e., lymphocytes) and categorized these proportions as low (0-10%), intermediate (11-59%), and high (60-100%). The news-worthy finding was that more TILs meant better disease-free and overall survival for triple-negative and HER2-positive cancers but worse outcomes for hormone-receptor-positive, HER2-negative cancers. This brings up a couple of questions: 1) are we missing something here by looking only at lymphocytes? and/or 2) does immune surveillance (and thus immunotherapy) play a completely different role in luminal-type breast cancers than conventional wisdom suggests? TIL next time...