PURPOSE The Merit-Based Incentive Payment System (MIPS) is currently the only federally mandated value-based payment model for oncologists. The weight of cost measures in MIPS has increased from 0% in 2017 to 30% in 2022. Given that cost measures are specialty-agnostic, specialties with greater costs of care such as oncology may be unfairly affected. We investigated the implications of incorporating cost measures into MIPS on physician reimbursements for oncologists and other physicians. METHODS We evaluated physicians scored on cost and quality in the 2018 MIPS using the Doctors and Clinicians database. We used multivariable Tobit regression to identify physician-level factors associated with cost and quality scores. We simulated composite MIPS scores and payment adjustments by applying the 2022 cost-quality weights to the 2018 category scores and compared changes across specialties. RESULTS Of 168,098 identified MIPS-participating physicians, 5,942 (3.5%) were oncologists. Oncologists had the lowest cost scores compared with other specialties (adjusted mean score, 58.4 for oncologists v 71.0 for nononcologists; difference, –12.66 [95% CI, –13.34 to –11.99]), while quality scores were similar (82.9 v 84.2; difference, –1.31 [95% CI, –2.65 to 0.03]). After the 2022 cost-quality reweighting, oncologists would receive a 4.3-point (95% CI, 4.58 to 4.04) reduction in composite MIPS scores, corresponding to a four-fold increase in magnitude of physician penalties ($4,233.41 US dollars [USD] in 2018 v $18,531.06 USD in 2022) and greater reduction in exceptional payment bonuses compared with physicians in other specialties (–42.8% [95% CI, –44.1 to –41.5] for oncologists v –23.6% [95% CI, –23.8 to –23.4] for others). CONCLUSION Oncologists will likely be disproportionally penalized after the incorporation of cost measures into MIPS. Specialty-specific recalibration of cost measures is needed to ensure that policy efforts to promote value-based care do not compromise health care quality and outcomes.