Update on my sister - endocrine therapy alone seems to have cured her DCIS
My sister was diagnosed with DCIS, grade 2, 100% ER+ about a year and a half ago. They originally recommended a mastectomy, which my sister was strongly opposed to doing. She connected with some women online who chose no treatment for DCIS except for endocrine therapy and decided to give it a try. As an IDC survivor, I wasn't really supportive of her decision. Amazingly, the treatment seems to have worked, and her imaging, including MRIs, are now completely clear. Apparently, there are studies being done on this, and one day endocrine therapy without surgery may be a recommended option for some women with DCIS. I think it's called the COMET study, if you want to look it up.
Her plan is to take the letrazole for 5 years, then decide whether to continue on it. What we don't want to happen is for her to get DCIS or even IDC in the future, and she's already been on 10 years of endocrine therapy. If breast cancer ever does come back, she plans to get something called cryoablation before considering lumpectomy or mastectomy.