Accelerated Partial Breast Irradiation

Patients should be carefully selected for APBI and properly informed of the current benefits and risks when considering APBI, WBI, and no radiation. Several APBI options exist and should be discussed in a multidisciplinary fashion to ensure optimal patient outcomes. There are risks and benefits to each of these approaches concerning effectiveness, side effect profile, patient access, and patient preference. These relevant techniques include:

1. External beam radiation therapy (EBRT) with 3-D conformal radiation, intensity modulated radiation therapy (IMRT) or protons
2. Brachytherapy with intercavitary or interstitial techniques
3. Per 2024 ASTRO guidelines, electron IORT is not recommended outside of a clinical trial or multi-institutional registry. Similarly, kilovoltage (kV) IORT alone (without WBI) is not recommended outside of a clinical trial or multi-institutional registry. Per 2022 ABS guidelines, recommendation for IORT is weak and considered appropriate for use on clinical trial only. This recommendation was initially published in the 2019 ABS guidelines and the 2022 update did not find sufficient evidence to justify changing this recommendation.

 

In consideration of the updated ASTRO and ABS guidelines, The American Society of Breast Surgeons recommends the following selection criteria when considering patients for treatment with APBI:

1. Age: Minimum of 40 years

2. Histology:

• All invasive subtypes, recognizing that ASTRO guidelines conditionally do not recommend APBI in lobular histology due to poor representation in clinical trials (and thus possible higher recurrence rates). ABS guidelines recommend APBI in all invasive subtypes. ▪ Ductal carcinoma in situ (DCIS)

3. Total tumor size (invasive and DCIS): less than or equal to 3 cm in size

4. T Size: Tis, T1, T2 (≤ 3 cm)

5. Margins:

• No tumor on ink for invasive tumors and invasive tumors with associated DCIS
• ≥ 2mm for DCIS

Note: ASTRO guidelines state that positive margins for both DCIS and invasive disease are a contraindication for APBI, however, do not specify the definition of a negative margin for invasive or in situ disease. ABS guidelines clearly specify no tumor on ink for invasive disease and ≥ 2mm for DCIS. Per ABS guidelines, PBI may be considered for selected patients with DCIS who have negative margins <2mm in the context of appropriate multidisciplinary and shared decision-making discussions.

6. Nodal Status: Negative Note: Omission of sentinel lymph node biopsy may affect candidacy for APBI as surgical staging is a key factor in formulating these recommendations. Shared decision-making and multidisciplinary discussion are recommended for the consideration of APBI following the omission of SLNB. We discourage the routine use of WBI following SLNB omission, as most patients who are candidates for SLNB omission likely would have had pathologically negative sentinel nodes and qualified for APBI as well.

7. Other Factors:

• Multifocal disease is allowed as long as the combined area of tumor is ≤3cm.
• Tumor may be estrogen receptor positive or estrogen receptor negative
• ABS guidelines allow for APBI for patients with tumors without extensive LVI, while recognizing the lack of a standardized definition for reporting LVI extent. ASTRO guidelines conditionally do not recommend ABPI in the setting of lymphovascular invasion due to underrepresentation in clinical trials, making it challenging to understand the implications of LVI on ipsilateral breast recurrence (IBR). Given the concerns for potential increased local recurrence rates, APBI should be considered with caution for patients with tumors exhibiting LVI.
• Patients should not be treated with APBI if they have a BRCA genetic mutation or other genetic mutation that confers an increased risk of breast cancer.
• There is no evidence to support use of APBI in male patients due to underrepresentation in clinical trials. ABS guidelines recommend offering APBI to men who have undergone breast conserving surgery and clinical and pathologic features otherwise appropriate for treatment with APBI.
• There is no contraindication to APBI in patients with history of contralateral breast cancer.
• In the absence of Level 1 data, repeat BCS with APBI may be considered for unifocal IBTRs less than 3 cm in size who have had no toxicity from prior radiation treatment. The time interval from prior radiation is a consideration.

8. Patient selection and counseling should be performed in a multidisciplinary fashion with collaboration between the treating surgeon and the treating radiation oncologist. These recommendations are intended as a guide to treat patients. Individual treatment decisions could allow treatment outside of the parameters listed above with appropriate multidisciplinary review and implementation of shared decision-making discussions with the patient.