Are plastic fumes carcinogenic?

Yes indeed! Plastic fumes have the potential to be harmful. May even cause cancer due, to their content of substances, like benzene and dioxins among others when they are burned or melted releasing toxic chemicals into the air which can elevate the chances of developing cancers in various parts of the body over time. It's important to make sure there's airflow and wear appropriate Personal Protective Equipment while avoiding direct contact to minimise these dangers.