96P Immune biomarkers on tissue microarray cores support the presence of adjacent tertiary lymphoid structures in soft tissue sarcoma

Immunotherapy has surfaced as a new treatment approach for certain soft tissue sarcomas with tertiary lymphoid structures (TLS). These ectopic lymphoid aggregates promote an immune response in the tumor microenvironment. Assessing TLS as a predictive biomarker at scale on patient specimens remains challenging. Even though tissue microarrays (TMAs) could facilitate this assessment, it is not clear if small TMA cores can represent associated TLS responses. We used multiplex immunohistochemistry to identify key components of TLS such as B cells, T cells, and dendritic cells on a single slide. Staining panels (CD20/CD79a, CD3, CD208, and PNAd) were applied to 80 cases on both TMAs and their corresponding full-faced sections from epithelioid sarcoma and dedifferentiated/well-differentiated liposarcoma arrays, as the training set. Additionally, 68 cases from the malignant peripheral nerve sheath tumor array were used as the validation set. TMAs were digitally scored for the number of immune cells, and cognate full-faced sections were visually evaluated for the presence of TLS. We observed that the Combined Immune Marker (defined as the presence of more than 24% CD3, or 0.51% CD20, or 0.14% CD208 cells on TMA cores) is a highly specific marker (100%) with moderate sensitivity (61%) to predict the existence of TLS on full-faced sections. Validation data indicate that the Combined Immune Marker remains highly specific (80%) but shows reduced sensitivity (27%) in detecting TLS. The Combined Immune Marker assessed on TMAs is a highly specific marker to detect the traces of TLS on full-faced sections. Therefore, despite the small area sampled, TMAs may be utilized to assess the clinical value of TLS on large datasets; particularly to validate the predictive capacity of TLS for immunotherapy benefit in sarcomas.