OBJECTIVE: Uterine papillary serous carcinoma (UPSC) is a variant of endometrial cancer that is aggressive and associated with poor outcomes. We sought to evaluate the cost effectiveness of carboplatin/paclitaxel alone versus carboplatin/paclitaxel with trastuzumab among patients with Her2/neu-positive advanced or recurrent UPSC. METHODS: We designed a Markov model in TreeAge Pro 2019 software to simulate management of a theoretical cohort of 4000 patients with Her2/neu-positive advanced or recurrent uterine papillary serous carcinoma (UPSC) followed for four years. In the carboplatin/paclitaxel with trastuzumab strategy, we included the cost of testing for Her2/neu status. We obtained all model inputs from the literature and a societal perspective was assumed. Outcomes included progression-free survival, progression, UPSC-specific mortality, cost, and quality-adjusted life years (QALYs). The intervention was considered cost effective if the incremental cost-effectiveness ratio (ICER) was below the willingness-to-pay threshold of $100,000 per QALY. Sensitivity analyses were used to determine the robustness of the results. RESULTS: In our theoretical cohort of 4000 women, treatment with the addition of trastuzumab resulted in 637 fewer deaths and 627 fewer cases of progression compared with treatment with carboplatin/paclitaxel alone. Treatment with trastuzumab was associated with an additional cost of $144,335,895, but was associated with an increase of 2065 QALYs. The ICER was $69,903 per QALY, which was below our willingness-to-pay threshold. Sensitivity analysis demonstrated that this treatment strategy was cost-effective until the cost of 6 months of treatment surpassed $38,505 (baseline input: $27,562). CONCLUSION: We found that the addition of trastuzumab to carboplatin/paclitaxel was a cost-effective treatment strategy for patients with advanced/recurrent Her2/neu-positive UPSC.