Tumor Size: Greater than 5 cm
Strong evidence supports the use of MRI imaging for a bone or soft tissue tumor of unknown etiology with a size greater than 5 cm to assist with obtaining a diagnosis and planning further treatment.

Rationale
Size is an important feature noted by clinicians on initial evaluation of a bone or soft tissue tumor. For malignancy, increasing size of the mass is correlated with adverse outcomes such as local recurrence and diminished overall survival, implying a relationship with tumor biology. The importance of size is also reflected in tumor classifications, such as the widely-used American Joint Committee on Cancer (AJCC) staging system which includes the maximal dimension of soft tissue sarcoma (5 and 10 cm) and bone sarcoma (8 cm) as one of the few characteristics used to determine cancer stage. A unifying feature of aggressive neoplasia is growth over time. By this reasoning, larger tumors may be more likely to represent a malignancy and require an assertive imaging investigation.

Our review focused on literature that discusses the relationship of size to an underlying malignancy, and the use of advanced imaging modalities to determine the cause and formulate a treatment plan. There were 5 high and 11 moderate quality studies evaluating the use of MR imaging for a bone or soft tissue tumor of unknown etiology with a mass of a certain size or depth to assist with obtaining a diagnosis or planning further treatment. High strength studies have evaluated the ability of MR imaging to differentiate benign from malignant tumors in a variety of locations in the axial (Matsumoto 2016) and appendicular (Liu 2011) regions and soft tissue masses with a variety of sizes, appearances (cystic or solid [Harish 2006]) and tissue types (fatty [Rougraff 1997], neurogenic [Zhang 2015], etc). Two high quality studies (Matsumoto 2016 and Zhang 2015) and 6 moderate quality studies (Calleja 2012, Chen 2009c, Chung 2012, Datir 2008, Gruber 2016, and Sen 2010) found MRI to have a moderate to strong relationship to histopathological results in determining malignancy of soft tissue tumors with a size of 5cm or larger. MRI is first option for staging malignant bone tumors and for evaluation of all indeterminate soft tissue tumors. Other imaging modalities (CT of the site, PET/CT, Tc 99m Bone Scan) are used in specific cases and should be implemented by, or with the guidance of, the treating oncology team.

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