"The Walking Dead" actor Erik Jensen has been diagnosed with stage four cancer ... this according to his wife, who has started a GoFundMe to help cover the rising costs. Erik's wife, Jessica Blank, said on the fundraiser her husband has stage four colorectal cancer ... and his diagnosis is coming a year and a half after he survived a brain aneurysm. She says Erik's cancer "has metastasized to his liver," but his doctors "have a shot at shrinking the tumors enough to do two very major surgeries and get them all out" ... adding how strong and resilient her husband is. Jessica points out that Erik, like countless other actors like him, has been financially affected by the "lack of streaming residuals" over the years ... not to mention the ongoing SAG-AFTRA strike, which has shut down most of Hollywood. She says they have mountains of medical costs, and now Erik's facing "serious risk" of losing SAG insurance ... which is why she's asking for his fans to help in any way they can. It seems like folks have already been supporting Erik during his health crisis -- he's received over $97k in a week, with a goal of $300k. Fans of the AMC series remember Erik portraying Steven Edwards, a doctor working at the post-apocalyptic medical facility, Grady Memorial Hospital. He's also worked on projects like "Mr. Robot," "The Equalizer," "Chicago P.D.," and "CSI."