回答
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You don't have to be admitted to a hospital for cancer. It can be treated in the outpatient now.
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Cancer doesn't require hospitalization. It can be treated in the outpatient setting nowadays.
「癌で入院する必要はなく、外来で治療できます」のように説明的に表すのが自然かと思いました。
入院する=is admitted to a hospital, is hospitalized
入院=admission to the hospital, hospitalization
外来=outpatient
癌治療の外来クリニック=cancer outpatient clinic