Background A biopsy is the final step in the diagnosis of sarcomas. Complete resection of the biopsy tract traditionally has been recommended in musculoskeletal oncology guidelines, as that tract is considered potentially seeded with tumor cells. However, to our knowledge, the frequency and implications of contamination of the biopsy tract-specifically with respect to the likelihood of local recurrence-and the factors that affect cell seeding are not well described. Questions/purposes We asked: (1) How often are biopsy tracts contaminated with pathologically detectable tumor cells at the time of tumor resection? (2) What factors, in particular biopsy type (open versus percutaneous), are associated with tumoral seeding? (3) Is biopsy tract contamination associated with local recurrence? Methods This is a retrospective study of a database with patient data collected from a single center between 2000 and 2013. We treated 221 patients with sarcomas. A total of 27 patients (12%) were excluded and 14 (6%) were lost to followup. One hundred eighty patients finally were included in the analysis who either had biopsies at our center (112) or biopsies at outside institutions (68). Of those performed at our center, 15 (13%) were open and 97 (87%) were percutaneous; of those at outside centers, those numbers were 47 (69%) and 21 (31%) respectively. Median followup was 40 months (range, 24-152 months). During the study period, we generally performed percutaneous biopsies as a standard practice for the diagnosis of bone and soft tissue sarcomas and open biopsies were done when the percutaneous procedure failed to provide a histologic characterization. The mean age of the population was 48 years (range, 7-87 years); 60% were male; 42% had bone sarcomas. Nineteen patients had preoperative radiotherapy and 56 had postoperative radiotherapy. Fifty-seven patients received neoadjuvant chemotherapy and 73 had Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research 1 editors and board members are on file with the publication and can be viewed on request. Each author certifies that his or her institution has or waived for the human protocol for this investigation and that all investigations were conducted in conformity with ethical and confidentiality principles of research. This work was performed at the Musculoskeletal Tumor Unit, Orthopaedics and Traumatology Department, at La Paz University Hospital, Madrid, Spain. We determined what proportion of biopsy tracts were contaminated by pathologic analysis of the biopsy tract specimen; during the period in question, our routine practice was to excise the biopsy tract whenever possible at the time of the definitive resection. Using the logistic regression test and Mantel-Haenszel test, we compared open wi...