Purpose
Although tumor infiltrating lymphocytes have been associated with response to neoadjuvant therapy, measurement is typically subjective, semi-quantitative and does not differentiate between subpopulations. Here we describe a quantitative objective method for analyzing lymphocyte subpopulations and assess their predictive value.
Methods
We develop a quantitative immunofluorescence (QIF) assay to measure stromal expression of CD3, CD8, and CD20 on one slide. We validate this assay by comparison to flow cytometry on tonsil and assess predictive value in breast cancer on a neoadjuvant cohort (n = 95). Then each marker is tested for prediction of pathologic complete response (pCR) compared to pathologist estimation of percentage lymphocyte infiltrate.
Results
Lymphocyte percentage and CD3, CD8, and CD20 proportions were similar between flow cytometry and QIF on tonsil. Pathologist TIL count predicted pCR (p = 0.043, OR: 4.77[1.05–21.6]) despite fair interobserver reproducibility (κ = 0.393). Stromal AQUA scores for CD3 (p = 0.023, OR: 2.51[1.13–5.57]), CD8 (p = 0.029, OR: 2.00[1.08–3.72]), and CD20 (p = 0.005, OR: 1.80[1.19–2.72]) predicted pCR in univariate analysis. CD20 AQUA score predicted pCR (p = 0.019, OR: 5.37[1.32–21.8]) independently of age, size, nuclear grade, nodal status, ER, PR, HER2, and Ki-67, whereas CD3, CD8, and pathologist estimation did not.
Conclusions
We have developed and validated an objective, quantitative assay measuring tumor infiltrating lymphocytes in breast cancer. While this work provides analytic validity, future larger studies will be required to prove clinical utility.