History of Growth: Soft Tissue Tumor
Moderate strength evidence supports that, in patients suspected of soft tissue tumor recurrence, an MRI of the tumor site can reliably identify neoplastic tissue and differentiate between solid and cystic areas.

Rationale
One aspect of a patient history that is important when evaluating a tumor of the bone or soft tissue is the general stability of the mass over time. Palpable masses that have been present and not enlarging for months or years are unlikely to represent a life-threatening malignancy, whereas tumors with rapid growth over a period of weeks may be concerning for an aggressive process. Much of the literature we found did not focus on the initial evaluation of a growing mass, but rather an attempt to distinguish recurrent tumor from a non-neoplastic process (post-operative scar, fluid collections, normal tissue). Although the clinical setting varied from our intended scenario, the question remained relevant, as the imaging was performed in attempt to determine the presence of a tumor in a patient with a concern for recurrent or residual sarcoma. One moderate quality study (Gingrich, 2017) reported on the ability of MRI to identify residual sarcoma after a prior resection and found 86.7% sensitivity, 57.9% specificity, and overall accuracy of 78.1%. One low quality study (Jiang, 2016) found that a soft tissue mass was a reliable indicator of tumor recurrence when an MRI was performed adjacent to a total joint arthroplasty, with 100% sensitivity and 96% specificity. One moderate quality study (Lehotska, 2013) used time-to-intensity curves to reflect the dynamic enhancement of soft tissue in contrast MRI and determined a positive predictive value of 95.7% and negative predictive value of 100% in their ability to diagnose recurrent sarcoma. One low quality study (Park, 2016) compared MRI to PET-CT and found that each could reliably detect soft tissue sarcoma recurrence and were statistically equivalent. They recommended MRI as the primary modality to investigate recurrence, with PET-CT as an additional option if the MRI was inconclusive.

In bone tumors, one moderate quality study (Pereira, 2014) reported that MRI was helpful and accurate at distinguishing solid and cystic components. The work group was concerned that a statement recommending MRI in all patients with a history of growth of a mass would result in a large number of unnecessary MRI scans. In our cumulative clinical experience, many patients report slow growth over time (a common history in benign entities such as lipomas) or may report a contradictory history of an enlarging mass which, by objective measures such as bony remodeling on conventional radiographs, is likely to be an inadvertent misrepresentation of tumor growth. Therefore, we recommend that an MRI be considered as an imperative study only when there is a clear history of rapid growth (such as a tumor doubling or tripling in size in a matter of weeks). Clinicians should use other measures, such as the appearance on conventional radiographs, presence of pain, size, and depth of the lesion as additional factors that can help with decision-making.

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