Koezy
While I am not an AME and I am in the UK, not Oz, I will do what I can...
Surgery - as long as you are fully recovered from the surgery and it does not cause restrictions (some breast patients have lymphoedema - swollen arm - that can restrict the use of that arm) then you should be OK from that point of view I would think.
Chemo - depends on what chemo you had, when and what effects it has had on you. From memory, the type of chemo usually used in breast patients does not have much in the way of long-term health problems. Bleomycin (used in lung and some testicular tumours for instance) can cause lung damage that then restricts your ability to absorb oxygen which causes issues when flying at altitude in unpressurised aircraft.
Long-term hormonal treatment - not sure if Tamoxifen and other hormone-modulators are permitted for pilots. You will need to check with your local AME.
Sorry I can't be more specific
HTH
BTD