I am currently receiving chemo for infiltrating ductal carcinoma. I was 44 when diagnosed last Sept. Mine was 6cm and growing along the blood vessels. Originally had lumpectomy, but followed 3 weeks later by mastectomy. Mine is stage IIIA with 1 lymph node involved. I am also ER/PR+ and Her2neu-. I also had some smaller tumors in what they called 'islands', so it was the right thing to have a mastectomy.
My treatment is 6 months of chemo, followed by radiation (not sure how long), then tamoxifen and then femara.
I would question them just giving you tamoxifen. Is a quadectomy the same as a lumpectomy? Usually, the younger you are, the more aggressive they are with treatment, so I would be surprised if you don't need chemo. It will all depend on what they find after surgery.
I have been very lucky to not have very bad side effects, just some nausea and tiredness (which is finally starting to go away). Therefore, I am able to work.
Everyone is different, but just know that we are all here for you to help get through this. This place has been a great help to me, particularly at the beginning.