Claims that COVID-19 vaccines cause or increase the risk of breast cancer and other miscellaneous health issues have circulated for years since the start of the pandemic, often fueled by exaggerated or misleading information meant to create fear around vaccination. In the source linked to this claim (American Cancer Society) detailing the connection between breast cancer and covid-19 vaccines, they explain that having breast cancer can hinder or weaken the effects of the covid vaccine, but it doesn’t say anything about the vaccine itself worsening or causing breast cancer. The other source listed on this claim (breastcancer.org) states clearly that there is no link between the COVID-19 vaccines and breast cancer risk or developing breast cancer.
Another source I found (BMC) was from a large population-based study done in South Korea, aiming to find the correlation between the risks of various cancers and receiving the COVID19 vaccine (1 year post vaccine). In this study, the researchers observed higher risks of six cancers one year after vaccination. The lowest HR (hazard ratio) on this list was the correlation between the vaccine and an increased risk of developing breast cancer, having such a low ratio it was not at all statistically significant, and the authors themselves said this evidence does not prove causation, only possible associations, and would need further research to prove any of these claims to be true. When the evidence is examined as a whole, rather than through fear-based misinformation, it becomes clear that there is no credible scientific link between COVID-19 vaccines and breast cancer risk. The claim that these vaccines cause cancer is therefore false.