Catholic position on standard medical care?

My father is refusing medical treatment for stage 1 melanoma.

Instead of the minor outpatient surgery that would easily remove the cancer, he is seeking a miraculous cure from Jesus.

This strikes me as far from a doctrinally correct Catholic position on such matters. I am hoping that others can help me with a principled Catholic response to his position.

Here are the facts as I understand them:

- My dad is in his early 80s and lives with my mom. Both are in good health and have no underlying serious medical conditions.
- A physician friend of my dad’s saw a brown spot under his eyelid when they were talking after Mass one day and recommended that my dad have it checked out.
- A biopsy revealed that the spot is melanoma.  However, it is stage 1, very superficial, and can be easily removed with a relatively minor outpatient surgery.
- The surgical procedure is not risky. The only potential downside is some minor disfiguration at the site of the cancer.
- Google searches indicate a very high 5-year survival rate for this cancer if it is surgically removed.
- I don’t know the prognosis if he leaves the melanoma untreated, but I am not aware of a good reason to leave it untreated.

Does my dad arguably have a moral obligation to go forward with the outpatient surgery to remove the melanoma?

Is it morally problematic if he does not get the surgery?

Thanks in advance!