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The Danish Breast Cancer Group (DBCG) affirmed a recommendation on partial breast irradiation (PBI) versus whole breast irradiation (WBI) for select low-risk patients, based on results of the group's recent .

Reporting in the , Birgitte Offersen, MD, PhD, of Aarhus University Hospital in Denmark, and colleagues randomized 865 patients who underwent breast-conservation surgery for relatively low-risk early cancer to PBI or WBI with 40 Gy/15 fractions. At 3 years of follow-up, the rate of breast induration, the primary outcome, was approximately halved in the PBI group (5.1% vs 9.7% for WBI, P=0.014).

In addition, there was no significant difference in locoregional recurrence. The 5-year risk was 0.7% for WBI vs 1.2% for PBI (P=0.47), the team said.

"PBI showed no increased risk of dyspigmentation, telangiectasia, edema, or pain, and patient satisfaction was high," the researchers wrote. "The findings are in accordance with other external-beam PBI trials. Moderately hypofractionated external-beam PBI is recommended as standard adjuvant therapy for selected patients with early breast cancer."

In the following interview, Offersen, who is also DBCG chair, discussed the details of the study, as well as new research exploring the option of eliminating radiation therapy.

What does your study add to previous studies comparing PBI with WBI in patients with breast cancer?

Offersen: The DBCG PBI trial is the first validation of the trial, where we have investigated patients with almost the exact same inclusion criteria, and we use the same radiation planning technique. It is always extremely important that randomized trials are externally validated, and that is the case here: using external beam 40 Gy/15 fractions for selected relatively low-risk breast cancer patients is safe.

As you noted, our trial documented a halved risk of breast induration and the same low risk of local recurrence. Indeed, the risk of local recurrence was lower in the treated breast (10 cases with local failure after radiation) as compared with the untreated contralateral breast, where 20 patients had a new primary breast cancer.

Overall, the local recurrence risk is extremely low, and even lower than the risk of a new primary. That indicates overtreatment. The treatment still leads to late effects as demonstrated in, for example, breast induration, and the patient needs to come for 3 weeks of treatment (in addition to having the cost of therapy).

How are you studying this issue of overtreatment?

Offersen: We have now initiated a trial where we randomize patients between partial breast radiation versus no radiation at all. The estimate is that those with partial breast irradiation will have a local recurrence risk of about 0.5% at 5 years, and those without treatment will have a risk likely around 2% (max 4%) at 5 years.

We know from previous DBCG studies that a local recurrence in "elderly" (i.e., over age 45) breast cancer patients treated for a relatively low-risk breast cancer, that a later local recurrence does not predict death from breast cancer. The trial with randomization to no treatment is the trial.

For what patients do you currently recommend PBI as standard adjuvant therapy?

Offersen: Since April 2016 all Danish breast cancer patients age 60 and older diagnosed with non-lobular breast cancer, max 20 mm, node-negative, ER+, HER2-neg, margin minimum 2 mm, are treated with partial breast irradiation at 40 Gy/15 fractions. Since March 2021, the age limit was lowered to 50 years.

You found that larger breast size was a significant risk for induration. For large-breasted patients treated with PBI, the risk of induration was about the same as for small-breasted patients treated with WBI (8% and 7%). What more can you tell us about this?

Offersen: [A paper on] the importance of breast size in relation to breast induration has just been accepted [and subsequently published] by , and we have further very interesting data where the age effect is also included in this equation -- to be submitted for the ESTRO 2023 conference.

What else would you like oncologists to understand about this issue?

Offersen: There are still radiation therapy [RT] centers in Europe and the United States where 5-6 weeks of RT is standard for these selected low-risk patients. They have whole-breast RT for 5 weeks, and then an extra boost dose for around 1 week. That is unnecessary for the patient, has more acute and late effects, and is costly.

Several randomized trials testing PBI have a control arm where the patients have whole breast RT followed by a boost. In the DBCG guidelines we use a boost very seldomly -- around 15% of breast cancer patients operated with breast conservation -- and we have local recurrence risks at the same low rates as in other trials/studies.

So the DBCG recommends 3 weeks of RT for all patients, and more selected use of boosts compared with many other RT centers.

Read the study here.