When doctors began using the drug sotorasib in 2021 with high expectations for its innovative approach to attacking lung cancer, retired medical technician Don Crosslin was an early beneficiary. Crosslin started the drug that July. His tumors shrank, then stabilized. But while the drug has helped keep him alive, its side effects have gradually narrowed the confines of his life, said Crosslin, 76, who lives in Ocala, Florida: “My appetite has been minimal. I’m very weak. I walk my dogs and get around a bit, but I haven’t been able to golf since last July.” He wonders whether he’d do better on a…