I have been exploring teas that can be recommended for Cancer.
One is called Indian Echinacea or Andrographis Paniculata . It is famous as Kalmegh in Sanskrit and Nelavembu in Tamil language. The leaves are bitter and potent. They are to be boiled in water and the juice consumed. More information on this plant is at Andrographis_Genus. There seem no dangerous side effects. Andrographis Paniculata has been used for centuries in Ayurveda and Siddha medicine.
Best way to get access to the herb would be to plant it in a pot for your garden / home. Then you can make the tea whenever needed. The plant grows well in the Indian weather. You can even see it growing wild in the roadsides. All you need to do is know how to spot the plant. Likely some nurseries can source it for you, although I have not yet seen it in the usual nurseries in Chennai. The photo is of its sister plant Andrographis Echioides.
I also recommend Ginger tea for cancer. This will be easier to source anywhere in the world. Ginger increases vitality.