Jason Priestley says his TV twin sister Shannen Doherty is a “fighter” amid her battle with terminal breast cancer.The actor was asked about his Beverly Hills, 90210 and BH90210 co-star, who revealed earlier this year that her cancer had returned — and progressed to stage 4 terminal cancer.“Last time I heard from her she was in pretty good spirits,” said Priestley, who revealed that he reaches out to Doherty “every few months just to check in on her and say hi.”He continued, “Shannen’s a real tough girl.