This registry trial is designed to track the local control rates and side effects of IORT, which will be implemented for women who are suitable partial breast irradiation (PBI) per the latest American Society of Radiation Oncology (ASTRO) guidelines.

Eligible patients will be referred for radiation oncology consultation by the operating surgeon. Patients will be presented with all radiation options and if they choose IORT, they will be offered enrollment onto the registry trial and consented accordingly. The registry will collect treatment data from the operation, radiation and pathology notes post IORT for each patient enrolled. Sources of research material, i.e. resected breast tissue and lymph nodes, will be obtained as part of routine clinical care. No additional tissue will be collected from patients due to enrollment on this registry trial. No additional studies will be performed outside of the routine standard of care.

Post treatment, the registry will collect data based on the standard of care follow up schedule. Follow-up visits will be scheduled 2-3 weeks post-operatively, as per standard of care, to review the final pathology and for the initial toxicity assessment. Patients found to have positive margins and/or lymph node involvement may require further surgery and/or additional external beam radiation. Additional follow-up visits with radiation oncology will be scheduled at 6 months and 1, 2, 3, 4, and 5 years following IORT. Toxicity will be scored using Common Terminology Criteria for Adverse Events (CTCAE) v4.03. Local control will be evaluated using clinical exam and semi-annual to annual mammograms. All such information will be tracked and recorded into the registry database.

Inclusion Criteria:

• Female gender
• Age ≥ 45
• cT1-2N0, <3.5cm invasive breast cancer, estrogen-receptor positive or DCIS of breast, Grade 1-2, mammographically detected, < 2.5 cm, estrogen-receptor positive
• Suitable for breast conserving surgery
• No contraindication to radiation
• Mammogram within 6 months of planned procedure
• Fitness for lumpectomy under general anesthesia
• Planned to receive IORT

Exclusion criteria

• Known axillary lymph node positive breast cancer (negative biopsy not required)
• Multicentric cancer in the same breast as diagnosed by clinical examination, mammography, ultrasound, MRI or pathologic assessment, not amenable to excision with negative margins with a single lumpectomy.
• Patients known to have BRCA 1/2 (breast cancer 1, breast cancer 2) gene
• Patients undergoing neoadjuvant chemotherapy
• Pregnancy

Female

Patients enrolled on this study will be planned for lumpectomy with or without sentinel node biopsy for early stage breast cancer. Patients will be evaluated by a radiation oncologist who specializes in the treatment of breast cancer and will be deemed to be eligible for IORT. Patients with a history of ipsilateral cancer and/or prior in-field radiation are eligible, as IORT would likely be less toxic than repeat whole or partial breast external beam radiation and can allow patients to avoid mastectomy who wish to do so.