Natalie Reichel is due for her next cancer therapy in March. But a contract fight between Mount Sinai Health System in New York City, where she gets care, and Anthem Blue Cross Blue Shield, whose network her insurance uses, has cast doubt on whether she’ll be able to get it on time. “I am feeling dubious,” said Reichel, 40. The dispute is about money: Mount Sinai says Anthem owes it more than $450 million in unpaid claims, while Anthem says Mount Sinai is demanding a 50% rate increase . Mount