The studies linking
vinyl chloride with cancer (particularly, liver angiosarcoma), pertains to
vinyl chloride MONOMER, which is the ingredient of polyvinyl chloride (PVC), the material used in shower curtains. PVC itself as a finished product seems to be inert and has not been implicated as a carcinogen. Unless you decide to burn your shower curtains (thereby releasing fumes of vinyl chloride monomers), I don't think that you're at an increased risk for developing cancer.