Hi Maria
My breast surgeon takes the lead - I see him every 6 months for at least five years and have the annual mammogram and an ultrasound if the radiologist on the day thinks that is necessary. If my surgeon or I have any concerns he shares the 6 monthly visits with the oncologist. He sends copies of the reports to the oncologist.
I guess it depends on who thinks they are in charge of your team and maybe their workload (read that as their need for constant income streams !).
If you are uncertain please pose the question to your surgeon. The oncologist may have said you are 'under control' so there is no need for additional visits.
Hope that helps. Keep in touch.
Summer :-)