My oncologist uses a nurse practitioner

I think the main point to be considered is the level of training and expertise of a medical provider for a specific situation.
An MD is a medical doctor who can go on to become a Specialist in a specific area. They do additional training and are board certified.
PAs have generalized course work and do not have coursework for specialized areas of medicine during their schooling. They can chose to work in a specific area and acquire on the job experience. NPs can be more specialized, but they are far from a Board-certified Specialist
Expertise matters. For example, last year my cancer pulmonologist referred me for a consult with interstitial disease pulmonologist regarding best choice in fibrosis drugs. The desk set me up with NP and I said no, I need MD because I have both lung cancer and pulmonary fibrosis. The new MD Specialist reviewed all my tests, scans, stress tests for last 3 years. He then gave me a diagnosis saying I had at least 3 reasons for shortness of breath. And he decided I should go on Oxygen and hold back on fibrosis drug. No NP/PA could do that.
It is a logical choice. If one is a "vanilla" follow-up case, that is one thing, but people with complex conditions where treatment choices need to be strategic, one cannot expect a person of significantly less training/experience to provide sufficient level of care.

@jeffmarc You nailed it with "be able to ask technical questions"
Routine follow up is one thing, but specific difficult issues requiring a judgement call based on knowledge and experience is another. There should be very clear guidelines determining the limitations of NPs or PAs. Complex patients with changing conditions should be followed by the Physician Specialist to avoid harm to the patient. I suspect people don't know that much about their condition and required treatment etc. It requires considerable investment of time to develop a real knowledge of one's condition.

My first follow ups were with the oncologist but now that I'm on the six month followup plan they're with an Oncology Nurse Practitioner. I'm fine with this. She takes up to an hour with me and thoroughly questions me about my progress. Any questions she doesn't know she refers to the oncologist and gets back to me in, at most, a day or two. Her followup is always thorough. All our interactions are thoroughly documented and I read the documentation for accuracy (I also read it for the oncologist as well). My oncologist is good but he's very busy so I prefer having more time with the NP vs. 15 minutes with the oncologist.

I initially saw an MD Oncologist every 90 days until I stopped ADT therapy (after 30 months). I still do blood work every 90 days but only see the Doc every other appointment and see an APRN on the alternate visits. I am a retired RN and I'm perfectly comfortable seeing nurse practitioners for many of my medical needs, especially when I have great confidence in their supervising physican.

Yes I see an NP in place of my oncologist because I’ve been doing very well going on three years now. My latest PSA was/is .15 and has been holding there for the most part. My oncologist said I can see him but since I’m doing so well that, while he oversees my test results that I see the NP, freeing him up for the more serious cases. Sounds good to me. Yes, I have concerns but I think we all do. My surgeon, and I didn’t have surgery, he supplied the chemical castrastion is also very happy. He told me at my last exam, that I had the lowest PSA of all the patients in the practice. Thanks Doc, and while good, when asked, yeah I’m #1, with the middle finger. I say try it and see.

My husband’s oncologist sees him every three months and she switches on and off with her NP. They both know everything about him. They work very closely together and we are lucky to have both of them.

I agree and my female PA has an attitude and takes 4-5 days to answer an email and after almost 2 yrs of not being able to to have sex she keeps telling me to be patient, at 79 that’s easy

@vic83 This is an excellent explanation. Thank You.