Website addresses (uniform resource locators [URLs]) are not case sensitive. As long as the underlying URL is valid, anyone clicking the link will be taken to the web page to which it points. However, there are times when a writer or publisher wishes to “expose” a URL in text. In that instance, URLs are normally presented as all lowercase.
This is true even when the URL contains an acronym that is normally capitalized.
The SEER database represents roughly 30% of the US population and uses data from 18 population-based registered cancer institutes (https://seer.cancer.gov).
Certain exceptions may apply when referring to websites by their name, rather than using the entire URL. For instance, the ClinicalTrials.gov website should be presented as shown, to help distinguish it from the journal Clinical Trials and because that presentation is a long-standing component of the trial registry’s identity.