Sharon Stone took to Instagram to announce she has a tumor that was only discovered after a misdiagnosis, a cautionary tale she hopes will encourage followers to “get a second opinion” when it comes to medical issues. “Just had another misdiagnosis and incorrect procedure,” the “Basic Instinct” star, 64, said Tuesday. She noted she was suffering “worsening pain” following a double epidural. “Went for a SECOND OPINION: I have a large fibroid tumor that must come out,” continued Stone. “Ladies in particular: Don’t get blown off … GET A SECOND OPINION … It can save your life.” Stone noted tha…