Questions & Answers on TIL-assessment


A : There is no minimal size to fibrosis or necrosis. In general, when we refer to fibrosis this is best illustrated by the so-called fibrotic focus which is sometimes seen in breast cancer (Ref.: Van den Eynden GG, et al. Histopathology. 2007 Oct;51(4):440-51).  When this is fibrotic focus is infiltrated by tumor cells, then this restriction does not apply. All mononuclear cells in areas of necrosis, irrespective of the size of this necrotic area are excluded.

A: All mononuclear cells (including lymphocytes and plasma cells) should be scored, but polymorphonuclear leukocytes are excluded.

A: This is indeed often found. The spatial importance of stromal TIls adjacent to tumorcells nests versus those stromal TILs that are not adjacent to the tumorcell nests is an active area of investigation right now. Digital pathology tools and/or machine learning algorithms are in full development and these may potentially answer this question one day.

A: There is no real cut-off for the TILs, as the prognostic as well as predictive importance of TILs are linear. In the early days, we used the term lymphocyte-predominant breast cancer, but this is actually not used anymore. So, TILs should be analyzed as a continuos variable in all studies. However, it is true that clinicians cut-offs for use in daily practice. In most studies the predictive importance is found at 5% TILs, while most significant prognostic importance is found with a cut-off of 30%.

A: No, formally, to analyze TILs you don't need immunohistochemistry since the validated method is based on morphology using an HE-slide. However, for practical reasons, when a biopsy is very crushed or badly fixed, or the slide is too thick, or when the tumorcells look like TILs (for example invasive lobular carcinoma) the TILs are not always easy to see, and instead of guessing whether there are TILs or not a stain may be useful. There is evidence that the TILs are mostly CD8-cells, so staining with CD8 recapitulates better the TILs than another stain, at this moment at least. There is plenty of research being done these days on characterizing the subtypes of TILs using immunohistochemistry and genomics, and this is in full development and we will learn more soon. For prognostic reasons, so far, subtyping does not seem to add to the outcome of patients compared to morphology alone, but much research on this is ongoing. So, in a final answer, morphology is sufficient, but a CD8 can help you when in doubt. Assessing the CD8 can be using the same method as for scoring the morphology, so proportion of stroma


A: No, if there’s no stromal invasion, no TILs should be scored. So, if there’s only LVI on the slide, no TILs should be scored.