Joseph Casias, 29, has sinus cancer and an inoperable brain tumor. Despite his condition, he has dutifully gone to work every day for the last five years at a Wal-Mart in Battle Creek, Michigan, where in 2008 he was named Associate of the Year. Casias is also a legal medical marijuana patient under Michigan state law. He uses marijuana with the recommendation of his doctor to relieve the effects of cancer. But Wal-Mart, the world’s largest public corporation, has no sympathy for his condition or…