A version of this article first appeared in CNBC's Healthy Returns newsletter, which brings the latest health-care news straight to your inbox. Subscribe here to receive future editions.Hello and happy Tuesday! Today, we're unpacking a shocking move from Pfizer. The pharmaceutical giant last week announced it would voluntarily withdraw its sickle cell disease therapy, Oxbryta, from worldwide markets — to the surprise of doctors, patients and investors.Here's why the drug is important: Oxbryta is one of at l ...