Almanac of Clinical Medicine, Vol 53, No 2 (2025)

Background: Dedifferentiated chondrosarcoma (DDCS) is a rare and extremely aggressive variant of mesenchymal bone tumors, with a biphasic structure represented by the classical chondrosarcoma elements, usually of low or intermediate grade, combined with a sharp transition to a highly malignant (high grade) non-cartilaginous sarcoma. The DDCS is associated with a poor outcome, low effectiveness of medical therapy and high mortality rates. One of promising areas of treatment for these tumors is immunotherapy, which requires a more profound understanding of the immunological status of the tumor and composition of its microenvironment.

Aim: To analyze the expression of PD-L1, CD4, CD8, CD20 and PU.1 markers in the inflammatory infiltrate of the tumor stroma in the samples of primary DDCS to search for new treatment and prognostic targets, as well as potential predictors of treatment efficacy.

Methods: We retrospectively analyzed the results of the immunohistochemical (IHC) studies of the tumor samples obtained from 42 patients with DDCS (18 men and 24 women aged 24 to 94 years; median age 65 years). The study samples of DDCS demonstrated two components, namely, well-differentiated chondrosarcoma and poorly differentiated non-cartilaginous sarcoma represented by pleomorphic undifferentiated sarcoma (n = 33), osteosarcoma (n = 6), rhabdomyosarcoma (n = 2) and angiosarcoma (n = 1). The IHC analysis was performed in the automated mode with a Ventana Bench Mark ULTRA IHC stainer (Ventana Medical Systems, USA) using an optimized protocol and anti-PD-L1 antibodies (clone SP142) and in the manual mode for staining with anti-PU.1, CD4, CD8 and CD20 antibodies. The PD-L1 expression was assessed separately in the dedifferentiated and chondroid components of the tumor. Samples containing PD-L1 expressing lymphocytes were counted separately.

Results: PD-L1 was expressed in the dedifferentiated component of 40% of the cases (17/42), in the chondroid component of 26% of the cases (11/42), and in both components in 17% of the cases (7/42). There was no association between PD-L1 expression in different tumor components and clinical and morphological characteristics of the disease. Median survival of the PD-L1 non-expressing patients was 68.6 months, while of those with the expression 7.7 months (p = 0.096). The mean macrophage count in the dedifferentiated tumor component was 17.3 ± 12.8%, that of CD4⁺ T-cells 4 ± 3.5%, CD8⁺ T-cells 4 ± 2.4%, and B cells 6.7 ± 3.8%. The analysis of an association between immune cell counts and clinical and morphological characteristics showed that higher tumor infiltration with B-cells was typical for an earlier stage of the disease (p = 0.045). The stromal markers studied did not have any prognostic significance, however there was a trend towards an unfavorable course of the disease (p = 0.112) for those with high macrophagal infiltration of the DDCS samples. The PU.1⁺ cell counts in the tumor stroma positively correlated with PD-L1 expression both in the chondroid (r = 0.357, p = 0.028) and in the dedifferentiated tumor components (r = 0.343, p = 0.033), as well as with the T cell numbers (r = 0.365, p = 0.026).

Conclusion: The results of our IHC studies on the expression of PD-L1, CD4, CD8, CD20, and PU.1 indicate the clinical and prognostic significance of the immune microenvironment of DDCS, opening additional prospects for predicting of the disease outcomes and development of immune therapies. Nevertheless, a more precise delineation of the clinical value of the identified markers requires that studies on larger patient samples should be continued.