Joining this conversation a little late. I too, assumed that if one is diagnosed with cancer, that the first step would be to see an oncologist. I was surprised that I was firstly referred to a general surgeon after my DCIS diagnosis.
The doctor and clinical nurse specialist at Breast Screening Queensland told me that I would firstly require surgery as part of my treatment. So I was directed to see my GP and get a referral to a general surgeon. The Breast Screening team also said I would see a radiation oncologist and a medical oncologist at some point. I do wonder if it works differently in the public system. Perhaps one may see the oncologist prior to being referred to a surgeon. Though I suppose it does make sense that the surgeon comes first, as the lesion needs to be removed and histopathology results of the removed tissue will determine the next step.