Establishing standardized immune phenotyping of metastatic melanoma by digital pathology
Bettina Sobottka1, Marta Nowak, Anja L. Frei, Martina Haberecker, Samuel Merki, Tumor Profiler Consortium, Mitchell P. Levesque, Reinhard Dummer, Holger Moch, and Viktor H. Koelzer1
1Correspondence to: firstname.lastname@example.org, email@example.com
CD8+ tumor-inﬁltrating T cells can be regarded as one of the most relevant predictive biomarkers in immune-oncology. Highly inﬁltrated tumors, referred to as inﬂamed (clinically “hot”), show the most favorable response to immune checkpoint inhibitors in contrast to tumors with a scarce immune inﬁltrate called immune desert or excluded (clinically “cold”). Nevertheless, quantitative and reproducible methods examining their prevalence within tumors are lacking. We therefore established a computational diagnostic algorithm to quantitatively measure spatial densities of tumor-inﬁltrating CD8+ T cells by digital pathology within the three known tumor compartments as recommended by the International Immuno-Oncology Biomarker Working Group in 116 prospective metastatic melanomas of the Swiss Tumor Proﬁler cohort. Workﬂow robustness was conﬁrmed in 33 samples of an independent retrospective validation cohort. The introduction of the intratumoral tumor center compartment proved to be most relevant for establishing an immune diagnosis in metastatic disease, independent of metastatic site. Cut-off values for reproducible classiﬁcation were deﬁned and successfully assigned densities into the respective immune diagnostic category in the validation cohort with high sensitivity, speciﬁcity, and precision. We provide a robust diagnostic algorithm based on intratumoral and stromal CD8+ T-cell densities in the tumor center compartment that translates spatial densities of tumor-inﬁltrating CD8+ T cells into the clinically relevant immune diagnostic categories “inﬂamed”, “excluded”, and “desert”. The consideration of the intratumoral tumor center compartment allows immune phenotyping in the clinically highly relevant setting of metastatic lesions, even if the invasive margin compartment is not captured in biopsy material.
- Laboratory Investigation, July 2021.