A proposal to end the need for Missourians to change doctors whenever they change HMOs is under debate in the state Senate. The Senate’s only doctor says cancer patients, pregnant women — and anybody else — should be able to keep their doctor even if their insurance company changes. Senator Marvin Singleton of Seneca favors the “any willing provider” concept, which says any doctor who qualifies to submit insurance claims should be allowed to submit them to whatever HMO insures his patient. Singleton says the priorities are wrong now. Some Senators worry that Singleton’s proposal will drive up health carecosts, especially to large companies or even to stategovernment, which provides coverage to its employees. The Senate will spend more time on his proposal later.