Background: It is important to understand the impact of the COVID-19 pandemic on cancer death rates in 2020 in the U.S. We estimated whether there were larger than expected changes in cancer mortality rates during March-December 2020 after accounting for temporal and seasonal patterns using data from January 2011-February 2020 by cancer type and age. Methods: We obtained death counts and underlying cause of death by cancer type, month/year (2011-2020), and age group from the National Center for Health Statistics and population estimates from the Census Bureau. Poisson regression was used to test for significant changes in cancer death rates from March-December 2020 compared to prior years. Results: After accounting for temporal trends and seasonal patterns, total cancer death rates were significantly lower than expected during March-December 2020 among 55-64-year-olds and ≥75-year-olds, but not in other age groups. Cancer death rates were 2% lower than expected from March-June among 55-64-year-olds, and 2-3% lower from March-July and December among ≥75-year-olds. Among ≥75-year-olds, colorectal cancer death rates were lower in March-June (RRs 0.94-0.96; p<0.05); however, lung cancer death rates were 5% lower across each month (all RRs 0.95, p<0.05). Conclusions: In the U.S., cancer death rates based on the underlying cause of death were broadly similar to expected rates during March-December 2020. However, cancer death rates were lower than expected among 55-64-year-olds and ≥75-year-olds, likely due to COVID-19 as a competing cause of death. Impact: Cancer mortality rates from 2020 should be interpreted with caution.