I think chemo is dependent on lymph node involved. Also need to know the behavioral characteristics of the tumor. I had some lymph node involvement (31 lymph nodes lit up but only 1 lymph node confirmed for cancer) and had the oncotype DX Assay test performed. I will give a number between 0 and 100 and my number was 13. I didn't need chemo. I was even told chemo would not benefit me because I already have a very low probability of recurrence. I also didn't need radiation therapy.

For my lumpectomy the radiologist injected radioactive isotope into the affected breast, so when I in surgery the surgeon used a giger counter. The reasoning behind this is cancer cells would absorbed the isotope. Since 31 lymph nodes lit up (the giger counter sounding off) there was evidence a cancer cell had been there. When pathology did tested the 31 lymph nodes only 1 lymph node was confirmed for cancer.

Linae, what do you mean when you say the lymph nodes lit up? During an MRI?

I was diagnosed with DCIS stage O, pathology from double mastectomy came back staged as Ia because invasive ductal carcinoma was found in the pathology. No chemo involved because of the size of the IDC tumor (only 1.2mm VERY small). Stage 1 is because no lymph nodes involved and the "a" based on size of tumor. My experience, hope this shed some light.