The phrase "without concern" denotes the absence of worry or care. There are various alternatives you can use instead of this cliched phrase in your writing, such as "indifferent," "reckless," "unmindful," or "heedless." Other synonyms of "without concern" include "apathetic," "unresponsive," "impassive," or "unaffected." If you want to convey a sense of negligence or disregard, you can consider using "unmindful," "inattentive," "careless," or "negligent" instead of "without concern." No matter which synonym you choose, it is essential to pick the right one that matches the context and conveys your message accurately and effectively.