INTRO: The physical decrements associated with cancer and its treatments can be attenuated with exercise. For this reason, exercise testing is essential to purposeful and individualized exercise prescriptions. Currently, the only treadmill protocol validated in cancer survivors is the University of Northern Colorado Cancer Rehabilitation Institute (CANCER) Treadmill Protocol. The Modified Bruce Treadmill Protocol (MB) is widely used for exercise testing in clinical settings and has been validated in healthy populations, but not cancer survivors. It is unknown whether the MB is an appropriate assessment tool compared to the validated cancer treadmill protocol. Multiple peak oxygen consumption (VO₂peak) predictive equations for the MB exist, however the accuracy of these equations in cancer survivors is unknown.  PURPOSE: To determine whether the MB yields as accurate VO₂peak values as the CANCER protocol in cancer survivors. The secondary purpose was to examine which MB predictive equation, if any, most accurately estimated VO₂peak in cancer survivors. METHODS: Twenty-two cancer survivors completed two VO₂peak treadmill tests, the CANCER and the MB protocol. One protocol was performed once per week in a randomized order. VO₂peak values were obtained via gas analysis using a research-grade metabolic cart. A paired samples t-test was performed to determine if differences occurred between the CANCER and MB VO₂peak values. A repeated measures ANOVA was performed to determine differences between four MB predictive VO₂peak equations. RESULTS: Due to its difficulty, one subject could not complete the MB, but completed the CANCER protocol.  There were statistically significant differences between VO₂peak values (mL·kg-1 ·min-1) found between the MB (26.38 ± 7.90) and CANCER protocol (28.65 ± 7.91) (p = 0.037). Furthermore, the American College of Sports Medicine (ACSM) walking/running equation from the last completed stage was the only predictive VO₂peak equation that was not statistically different than actual VO₂peak (p = 0.930) for the MB. CONCLUSION: Findings from this preliminary data suggest the MB underestimates VO₂peak in cancer survivors and may be too difficult for some to complete. This data proposes the MB may not be suitable to determine VO₂peak in cancer survivors.