The Cells Around the Tumor May Hold the Key to Improving Immunotherapy in Synovial Sarcoma

A new study published in PLOS One by Ji-Yong Sung, Jin-Hong Kim, and Yi-Jun Kim from Seoul National University and Ewha Womans University, South Korea, examines a type of cell found in the tissue surrounding tumors, called cancer-associated fibroblasts (CAFs), and asks whether they can predict how a sarcoma patient will respond to immunotherapy.

What Are Cancer-Associated Fibroblasts

Tumors are not made up of cancer cells alone. They exist within a surrounding environment of other cell types that can either help or hinder the immune system’s ability to fight the cancer. CAFs are among the most important of these surrounding cells. Depending on their subtype, they can promote tumor growth, suppress immune activity, or help recruit immune cells to attack the cancer. Three subtypes have been identified: myoCAFs, which drive tumor growth and tissue remodeling; infCAFs, which promote inflammation and immune suppression; and apCAFs, which help activate T cells against the tumor.

What the Study Found

Using single-cell data from synovial sarcoma and osteosarcoma alongside data from over 200 sarcoma patients in The Cancer Genome Atlas, the researchers found that myoCAFs are the dominant cell type surrounding synovial sarcoma tumors, more so than in other sarcoma subtypes. Patients with higher expression of the myoCAF-associated gene signature (SIG134) had a poorer prognosis, suggesting that a myoCAF-heavy tumor environment may be linked to worse outcomes in synovial sarcoma.

The study also identified a four-gene signature called SIG4, made up of MDK, SDC2, LRP1, and NCL, derived from signaling patterns between infCAFs in metastatic sarcoma. High expression of these genes was significantly associated with shorter survival and poorer immunotherapy response across multiple sarcoma subtypes in external validation data.

Looking Ahead

Synovial sarcoma has historically shown poor responses to checkpoint immunotherapy drugs. This study offers a potential explanation rooted not in the cancer cells themselves, but in the environment surrounding them. If signatures like SIG4 are validated in future clinical studies, they could one day help identify which synovial sarcoma patients are most likely to benefit from immunotherapy and which may need a different approach entirely. The authors are clear that this is a computational study and that experimental validation is still needed, but the inclusion of synovial sarcoma-specific data makes it a meaningful contribution to understanding why this disease behaves the way it does.

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