Neoadjuvant radiation influences the pseudocapsule in soft tissue sarcoma: A histopathologic and radiographic evaluation

A pseudocapsule surrounds soft tissue sarcoma (STS). Its composition, response to neoadjuvant radiation, and clinical significance are poorly understood.Seventeen cases of high-grade undifferentiated pleomorphic sarcoma (UPS) were reviewed, ten of which were treated with neoadjuvant radiation. Magnetic resonance imaging (MRI) studies, pathology slides, and patient records were reviewed.Irradiated pseudocapsules were well-demarcated with fewer viable tumor cells and were thicker on both pathology and MRI measurements when compared to non-irradiated pseudocapsules (p < 0.001, p = 0.04, respectively). Pseudocapsule mean pathology width (MPW) was positively correlated with tumor necrosis percentage (p = 0.044), and negatively correlated with mitotic rate (p = 0.043), though pseudocapsule width measured on MRI did not correlate with these prognostic factors. Despite an evident treatment response to neoadjuvant radiation, viable tumor cells were present within the pseudocapsule and the surrounding healthy tissue.The pseudocapsule in STS responds to radiation and there appears to be a correlation between pseudocapsule width and tumor necrosis and mitotic activity. As viable tumor cells are present beyond the pseudocapsule, surgeons should remain cautious in determining margins of resection in STS when using the pseudocapsule as a palpable landmark. This novel study is the most detailed to date to describe the histopathologic and radiographic characteristics of the STS pseudocapsule. Further studies are needed to determine the clinical significance of the pseudocapsule.