Can zakat be given to someone who has cancer and is receiving donations for treatment?

Someone’s eligibility is based on whether they would qualify under the categories of the ayah as from al-fuqaraa or al-masakeen. In other words, if they lack the financial resources to meet their most basic needs, OR have basic needs but cannot meet other essential and common needs (which include housing, transportation, etc.). In this case, sources of income such as alimony or child support would be part of the consideration of access to wealth.

If they are eligible, you may give your zakat money for their cancer treatment, and they do not need to be informed as the Zakat-eligible recipient, that the money they are receiving is Zakat money.