Identification of Malignancy in Peritumoral Edema in Soft Tissue Sarcoma: A Novel Targeted Molecular Approach

Peritumoral edema on staging magnetic resonance imaging (MRI) is associated with higher local recurrence in soft tissue sarcoma (STS). This may relate to the presence of satellite malignant cells that are difficult to distinguish from benign atypia, leading to over- or undertreatment. This study evaluated a novel targeted molecular approach to identify malignancy in STS peritumoral planes as a means to improve personalized care.

In the targeted molecular approach, whole-exome sequencing was employed to identify tumor-specific variants (TSVs), and peritumoral planes were assayed for malignancy, defined as two or more TSVs/plane, using droplet digital polymerase chain reaction (PCR). Feasibility was evaluated using a retrospective cohort (n = 8) in which planes with cellular atypia were tested. A prospective cohort (n = 8) then assayed all peritumoral planes with radiologic edema.

The targeted molecular approach identified malignancy in three of eight cases with cellular atypia of unknown significance (37.5%) and five of eight cases with peritumoral edema on staging MRI (62.5%). Peritumoral regions were heterogeneous; in none of the malignant cases did all sampled planes have evidence of tumor. Malignancy was also identified in regions without cellular atypia. Both cases with a local recurrence had molecular evidence of malignancy outside the main mass despite R0 margins.

This study describes a novel personalized approach to detect malignancy in peritumoral regions in STS and is the first to identify molecular evidence of tumor outside the main mass. While development of a clinical tool is underway, these findings support the current approach of treating all peritumoral edema as malignant.