The IDEA Study (Individualized Decisions for Endocrine Therapy Alone)

This study's primary aim is to determine rates of recurrence with the innovative approach of
considering tumor biology to select patients who may avoid radiation, with restriction of
eligibility to women aged 50-69 with hormone-sensitive, Her2-negative tumors with Oncotype-DX
RS ≤ 18 who plan to receive endocrine therapy. In this way, this study seeks to collect
prospective data supporting the idea that this is a population at low risk of LRR in whom
omission of adjuvant radiation is reasonable.

Inclusion Criteria:

- Postmenopausal status, as defined by (a) patients age 60 or greater, or, (b) patients
age 50-69 with either (a) s/p bilateral oophorectomy, or, (b) intact uterus without
menses in the past 12 months, or, (c) biochemical confirmation of postmenopausal
status.

- Histopathological confirmation of Stage 1 (pT1N0M0) invasive breast cancer status post
breast conserving surgery

- Negative axillary nodes (isolated tumor cells with no cluster measuring >0.2mm
allowed)

- Allowable options for axillary staging include:

- Sentinel node biopsy only

- Sentinel node biopsy followed by axillary dissection

- Axillary dissection only

- Margins of excision ≥2mm

- ER+, PR+, Her2 - using the current College of American Pathologists guidelines

- Oncotype-DX RS ≤ 18

- Disease must be unifocal on clinical, radiologic, and pathologic examination

- Registration within 90 days of last surgical procedure for breast cancer treatment

- Patient must willingly sign study specific informed consent prior to study entry

- Patient must be a candidate for and willing to take endocrine therapy for minimum of 5
years (aromatase inhibitor or tamoxifen). Patients who have already begun endocrine
therapy after lumpectomy are eligible.

- Patient must have had breast imaging (mammogram or MRI) of the ipsilateral breast
within 6 months and contralateral breast within 1 year of study entry.

- Patient must have Zubrod performance status 0-2

Exclusion Criteria:

- Evidence of multifocal or multicentric breast cancer that has not been biopsy-proven
negative. Note that MRI is not required for this study, but if performed, evidence of
disease beyond the site of the primary tumor in the ipsilateral breast or in the
contralateral breast must be biopsy-proven not to be malignant before registration.

- Metastatic disease. Note that no specific staging studies are mandated, but any
studies performed must not provide clear evidence of metastatic spread.

- Previous radiation therapy to the breast region

- Prior DCIS or invasive breast cancer

- Bilateral breast cancer

- Prior non-breast invasive malignancy other than non-melanoma skin cancer, unless there
has been no evidence of disease for at least 5 years

- Known carrier of a mutation known to predispose towards breast cancer development
(including BRCA-1 and BRCA-2). Note: testing for mutation status is not required for
this protocol; this criterion applies only to patients who have been tested and have
known carrier status.