ASTRO Updates Partial Breast Irradiation Guidance in Early Breast Cancer

The American Society for Radiation Oncology (ASTRO) has issued an updated clinical practice guideline on partial breast irradiation for women with early-stage invasive breast cancer or ductal carcinoma in situ (DCIS). 

The 2023 guideline, which replaces the 2017 recommendations, factors in new clinical trial data that consistently show no significant differences in overall survival, cancer-free survival, and recurrence in the same breast among patients who receive partial breast irradiation compared with whole breast irradiation. The data also indicate similar or improved side effects with partial vs whole breast irradiation.

To develop the 2023 recommendations, the Agency for Healthcare Research and Quality (AHRQ) conducted a systematic review assessing the latest clinical trial evidence, and ASTRO assembled an expert task force to determine best practices for using partial breast irradiation.

"There have been more than 10,000 women included in these randomized controlled trials, with 10 years of follow-up showing equivalency in tumor control between partial breast and whole breast radiation for appropriately selected patients," Simona Shaitelman, MD, vice chair of the guideline task force, said in a news release.

"These data should be driving a change in practice, and partial breast radiation should be a larger part of the dialogue when we consult with patients on decisions about how best to treat their early-stage breast cancer," added Shaitelman, professor of breast radiation oncology at the University of Texas MD Anderson Cancer Center in Houston.

What's in the New Guidelines?

For patients with early-stage, node-negative invasive breast cancer, the updated guideline strongly recommends partial breast irradiation instead of whole breast irradiation if the patient has favorable clinical features and tumor characteristics, including grade 1 or 2 disease, estrogen receptor (ER)-positive status, small tumor size, and age 40 or older.

In contrast, the 2017 guideline considered patients aged 50 and older suitable for partial breast irradiation and considered those in their 40s who met certain pathologic criteria "cautionary."

The updated guideline also conditionally recommends partial over whole breast irradiation if the patient has risk factors that indicate a higher likelihood of recurrence, such as grade 3 disease, ER-negative histology, or larger tumor size.

The task force does not recommend partial breast irradiation for patients with positive lymph nodes, positive surgical margins, or germline BRCA1/2 mutations or patients under 40. 

Given the lack of robust data in patients with less favorable risk features, such as lymphovascular invasion or lobular histology, partial breast irradiation is conditionally not recommended for these patients.

For DCIS, the updated recommendations mirror those for early-stage breast cancer, with partial breast irradiation strongly recommended as an alternative to whole breast irradiation among patients with favorable clinical and tumor features, such as grade 1 or 2 disease and ER-positive status. Partial breast irradiation is conditionally recommended for higher grade disease or larger tumors, and not recommended for patients with positive surgical margins, BRCA mutations or those younger than 40.

In addition to relevant patient populations, the updated guidelines also address techniques and best practices for delivering partial breast irradiation.

Recommended partial breast irradiation techniques include 3-D conformal radiation therapy, intensity modulated radiation therapy, and multicatheter interstitial brachytherapy, given the evidence showing similar long-term rates of ipsilateral breast recurrence compared with whole breast irradiation.

Single-entry catheter brachytherapy is conditionally recommended, and intraoperative radiation therapy techniques are not recommended unless integrated into a prospective clinical trial or multi-institutional registry.

The guideline also outlines optimal dose, fractionation, target volume, and treatment modality with different partial breast irradiation techniques, taking toxicities and cosmesis into consideration.

"We hope that by laying out the evidence from these major trials and providing guidance on how to administer partial breast radiation, the guideline can help more oncologists feel comfortable offering this option to their patients as an alternative to whole breast radiation," Janice Lyons, MD, of University Hospitals Seidman Cancer Center, Cleveland, Ohio, and chair of the guideline task force, said in the news release.

The guideline, developed in collaboration with the American Society of Clinical Oncology and the Society of Surgical Oncology, has been endorsed by the Canadian Association of Radiation Oncology, the European Society for Radiotherapy and Oncology, and the Royal Australian and New Zealand College of Radiologists. Guideline development was funded by ASTRO and the systematic evidence review was funded by the Patient-Centered Outcomes Research Institute. Disclosures for the task force are available with the original article.