Formalin fixation could interfere with the clinical assessment of the tumor-free margin in tumor surgery: magnetic resonance imaging-based study.

OBJECTIVES: The tumor-free margin in bone and soft-tissue cancer is a key factor for subsequent treatment. While flattening and shrinkage of specimens after formalin fixation have been described in breast cancer, there are no data for bone and soft tissue sarcoma. Fixation could interfere with the accuracy of the assessment of the tumor-free margin. METHODS: The influence of formalin fixation was assessed on forelimb specimens in a preclinical porcine model. The specimens were subjected to magnetic resonance imaging before and after formalin fixation. Weight, width and height of the specimen were measured and different consecutive volumes (total, muscles, bones and fatty tissue) were obtained by segmentation. RESULTS: After formalin fixation, the weight increased, total volume and muscle volume slightly increased while bone did not change and fatty tissue decreased. The width of the specimens increased while their height decreased. CONCLUSIONS: Formalin fixation caused slight muscle expansion, fatty tissue shrinkage and flattening of the specimen. These changes could interfere with the assessment of the tumor-free margin in clinical practice.