We investigate social media discourses on the relationship between cancer and COVID-19 vaccines focusing on the key textual topics, themes reflecting the voice of cancer community, authors who contribute to the discourse, and valence toward vaccines. We analyzed 6,427 tweets about cancer and COVID-19 vaccines, posted from when vaccines were approved in the U.S. (December 2020) to the February 2022. We mixed quantitative text mining, manual coding and statistical analysis, and inductive qualitative thematic analysis. Nearly 16% of the tweets posted by a cancer community member mentioned about refusal or delay of their vaccination at the state/local level during the initial rollout despite the CDC's recommendation to prioritize adults with high-risk medical conditions. Most tweets posted by cancer patients (pro = 82.4% vs. anti = 5.1%) and caregivers (pro = 89.2% vs. anti = 4.2%) showed positive valence toward vaccines and advocated for vaccine uptake increase among cancer patients and the general population. Vaccine hesitancy, self-reported adverse events, and COVID-19 disruption of cancer treatment also appeared as key themes. The cancer community called for actions to improve vaccination procedures to become safe and accessible especially for elderly cancer patients, develop COVID-19 vaccines suitable for varying type, stage, and treatment of cancer, and advance cancer vaccines. Future research should continue surveilling conversations around continuous impacts of COVID-19 interference with the cancer control continuum, beyond vaccination, focusing on the voice and concern of cancer community.