(Reuters) - New data is likely to prompt doctors to abandon Bristol-Myers Squibb's immunotherapy Opdivo in favor of Merck & Co's rival Keytruda in a large segment of the lucrative lung cancer market, analysts said on Monday. The results of a closely watched clinical trial sent Bristol's shares plunging 10 percent. The data, presented at a medical meeting on Sunday, showed that lung cancer patients fared worse on Opdivo than those on chemotherapy. Merck shares rose nearly 2 percent on stron