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Background: Concern persists regarding percutaneous core needle biopsy (CNB) of a potentially malignant lesion of the retroperitoneum due to the perceived risk of immediate complications and adverse oncologic outcomes, including needle tract seeding (NTS)., Objective: The aim of this study was to evaluate the incidence of (1) early complications and (2) NTS following CNB of suspected retroperitoneal sarcoma (RPS)., Methods: Patients who underwent CNB of an RP mass with pre-biopsy suspicion of sarcoma were identified from a prospective database at two centers: (1) Princess Margaret Cancer Centre/Mount Sinai Hospital, Toronto (2009-2015); and (2) The Ottawa Hospital (1999-2015). Early complications, including bleeding, pain, infection, and organ injury, were recorded. Instances of NTS were identified from long-term follow-up of patients who underwent resection of primary RPS at these two centers after initial CNB (1996-2013)., Results: Of 358 percutaneous CNBs of suspected RPS performed over the study period, 7 (2.0%) resulted in minor bleeding with no transfusion, 3 (0.8%) resulted in significant pain, 1 (0.3%) resulted in unplanned admission to hospital for observation, and 1 (0.3%) resulted in a pneumothorax. There were no infections. In 203 patients who underwent resection of RPS following CNB, crude cumulative local recurrence was 24% at 5 years. At a median follow-up of 44 months, there was one case of NTS (approximately 0.5%)., Conclusion: This large bi-institutional experience with CNB of an RP mass demonstrates that both the early complication rate and the incidence of NTS are very low. Physicians and patients can be reassured that the benefits of CNB in diagnosing sarcoma and determining its histologic subtype and grade far outweigh the risks.

To evaluate histologic subtype and grade, which in turn guide the decision making for multimodality therapy, the workup of suspected sarcoma requires more material than can be obtained from a fine-needle aspiration. Either open or percutaneous core needle biopsy is indicated before a management decision is made. Percutaneous biopsy of a potentially malignant lesion is controversial, given the perceived potential for tumor seeding along the needle tract. However, the evidence that the latter is a significant risk is weak at best. To the authors' knowledge, among cases of patients with extremity sarcoma who have undergone core needle biopsy, only a few cases of needle tract seeding have been reported to date. Although en bloc excision of the needle tract with the primary tumor is often performed, this practice is not associated with improved oncologic outcomes; the evidence for excision of the needle tract is poor. For patients with gastrointestinal stromal tumors, there is a theoretical risk of peritoneal dissemination after percutaneous biopsy, but to the authors' knowledge this remains unproven. Although endoscopic ultrasound is the preferred route for biopsy among patients with gastrointestinal stromal tumors, percutaneous biopsy is indicated if endoscopic ultrasound is unsuitable or unavailable. In the setting of retroperitoneal sarcoma, a review of pooled data from 4 large tertiary care referral centers demonstrated a risk of needle tract seeding of 0.37%. The authors concluded that the benefits of pretreatment biopsy in patients with mesenchymal tumors outweigh the potential risks of needle tract seeding. Cancer 2017;123:560-567. © 2016 American Cancer Society., (© 2016 American Cancer Society.)