Who is the patron saint of cancer patients?

Peregrine Laziosi is the one most people mean. A fourteenth-century Servite friar, he is said to have had a tumour on his leg that was due to be amputated, and to have recovered after a night of prayer before a crucifix.

Many parishes hold a Saint Peregrine Mass or healing service for the sick. They are usually well attended and specifically for people in your situation, which some patients find matters more than the devotion itself. Ask your parish whether one is held near you.

Others commonly invoked include Our Lady of Lourdes, whose feast on 11 February is also the World Day of the Sick; Saint Luke, traditionally a physician; Saint Camillus de Lellis and Saint John of God, both associated with care of the sick; Saint Damien of Molokai for people who feel isolated by illness; and Saint Jude in situations that feel hopeless.

Asking a saint to pray for you is intercession, meaning asking someone to pray alongside you. It is not presented in Catholic teaching as an alternative channel of treatment, and the Catechism notes that "even the most intense prayers do not always obtain the healing of all illnesses."

If someone is charging significant money for a healing product or a guaranteed intercession, treat that as a commercial transaction rather than a devotion.