Primary Biliary Cirrhosis. Up to 95% of primary biliary cirrhosis (PBC) cases occur in women, usually around age 50. In people with PBC, the immune system attacks and destroys cells in the liverâs bile ducts. Like many autoimmune disorders, the causes of PBC are unknown.rimary Biliary Cirrhosis. Up to 95% of primary biliary cirrhosis (PBC) cases occur in women, usually around age 50. In people with PBC, the immune system attacks and destroys cells in the liverâs bile ducts. Like many autoimmune disorders, the causes of PBC are unknown.