 PCBs may play a role in the development of cancers of the immune system because some tests of laboratory animals subjected to very high doses of PCBs have shown effects on the animals' immune system, and some studies of human populations have reported an association between environmental levels of PCBs and immune response.In 1865 the first "PCB-like" chemical was discovered, and was found to be a byproduct of coal tar.Years later in 1881, German chemists synthesized the first PCB in a laboratory.