Does a DNR order conflict with Catholic teaching?

Not in itself. The Ethical and Religious Directives address this in a footnote to the directive on proportionate and disproportionate means.

It says that a patient, or their surrogate, "may request a Do Not Attempt Resuscitation order (DNAR) if, in close consultation with the health care team, he or she determines that resuscitative measures would not offer a reasonable hope of benefit or entail excessive burden."

The same footnote adds the reassurance that families most need: "It must be clear to patients, families, and caregivers that a DNAR order does not mean that ongoing care should cease; on the contrary, ordinary/proportionate care should continue."

So a DNR is not a decision to stop being cared for. Symptom control, nursing, comfort measures, and everything else continue exactly as before.

What the teaching does not permit is acting with the intention of causing death. The distinction throughout is about intention rather than outcome.

Whether resuscitation would be likely to benefit you is a medical question, and it depends on your diagnosis and your overall condition. Ask your oncology team what they would realistically expect, and ask for a chaplain or an ethics consultation if it would help you think it through.