Introduction: The incidence of metastasis in patients with cT1a masses is an exceedingly rare event. However, guidelines recommend some form of thoracic imaging for patients with newly diagnosed renal masses. Screening for thoracic metastasis can be accomplished with either a chest x-ray (CXR) or CT of the thorax (CTT) and guidelines are agnostic to type of imaging modality utilized. Therefore, we designed a study evaluating the cost-effectiveness of CXR followed by selective CTT compared with that of universal CTT staging. Methods: Using TreeAgePro 2019 software, we developed a clinical decision tree to estimate the thoracic metastasis detection rate and cost of a selective CTT strategy compared to universal CTT at the time of initial staging in patients with cT1a renal masses. Patients who had a positive CXR subsequently had a CTT to confirm the positive result. In the universal CTT arm all patients were staged with a CTT. Model probabilities were derived from published literature. Direct costs were obtained from the Medicare procedure database. Our primary outcomes were proportion of true cancers detected, accuracy of and the incremental cost effectiveness ratio (ICER) which evaluates the incremental cost per additional true positive (TP) metastasis identified. Results: The universal CTT strategy resulted in a greater proportion of true cancers detected (TP/baseline prevalence of pulmonary metastases) (93.9%) when compared to CXR (66.7%). However, when the imaging tests were assessed by accuracy (true positive + true negative), the selective CTT staging strategy was found to be more accurate at 93.2% compared to 76.7% for the universal CTT staging strategy. This is balanced by a proportion of false positive (23.2%) in the universal CTT arm compared with 6.6% in the CXR based screening arm. To identify an additional metastasis diagnosed by a universal CTT that would be missed by a CXR based screening strategy would cost $59,931 . Our results are robust to sensitivity analyses evaluating the baseline prevalence of metastasis, but the ICER does vary considerably when the sensitivity of CT imaging was varied. Conclusions: Our study demonstrates that while a greater proportion of true positive tests are obtained using a universal CT staging strategy this is at the expense of a greater false positive rate. Given the low pretest probability of chest metastasis in patients with cT1a renal masses, there is considerable additional cost associated with screening this population with CTT to identify the few masses that would be missed with CXR based screening protocols. SOURCE OF Funding: None
