Integrated Boost Can Be Standard after Lumpectomy

Hypofractionated (HF) whole-breast irradiation with simultaneous integrated boost (SIB) can be considered a standard of care for adjuvant radiotherapy after breast conserving surgery, new data suggests.

David Krug, MD, with the University Hospital Schleswig-Holstein in Kiel, Germany, presented the findings of the primary analysis of the HYPOSIB Trial at the American Society for Radiation Oncology (ASTRO) 2024 Annual Meeting on Sunday. HYPOSIB is a phase 3 randomized, controlled, European, multicenter, noninferiority trial.

Two-Arm Design

Patients (n = 2,324) were randomized 1-to-1 either to the experimental arm (40 Gy to the breast; 48 Gy to the tumor bed in 16 fractions) or to the control group (physician’s choice between conventional fractionation with SIB or sequential tumor bed boost [seqB], or HF with seqB) from 2015-2019, which were the standard-of-care options in Germany at the time of the study.

Patients were, on average, 57.6 years old, and most were low-risk and post-menopausal. About 20% had grade 3 tumors, Krug said. 

The primary endpoint was disease-free survival at 5 years. Median follow-up was 52.9 months. Secondary endpoints included safety, time to local tumor recurrence, overall survival, quality of life, and cosmetic satisfaction.

Noninferiority Established

Disease-free survival at 5 years was 92% in the experimental arm and 92.2% in the control arm (hazard ratio [HR] =1.1), thus establishing the experimental arm was noninferior. The trial’s bar for noninferiority was less than or equal to a HR of 1.76. Overall survival at 5 years was 98.2% in the experimental arm and 97.9% in the standard arm (HR = 0.78). Local control at 5 years was 98.2% in the experimental arm and 98% in the control arm (HR = 1.08).

Krug said the data were clear: “Moderate hypofractionation with simultaneous integrated boost can be considered a standard of care.” 

He noted that the HYPOSIB trial is one of three large trials, along with IMPORT HIGH  and RTOG 1005 , that have shown HF with SIB is feasible and safe. He acknowledged that the patients in the HYPOSIB trial were lower-risk than the patients in the others.

Trial Supports Previous Results

“Hypofractionated breast radiation with integrated boosts are newer in the treatment of breast cancer compared with sequential boosts,” Kimberly Corbin, MD, with Mayo Clinic Alix School of Medicine in Rochester, Minnesota, said in an interview. “We’ve seen a couple of clinical trials published showing noninferior outcomes with sequential boost, so this trial adds to that body of literature supporting very good outcomes for cancer control and toxicity.” 

Longer-term analysis of outcomes for toxicity, quality of life, and cosmetic results are still to come, she said.

Some radiation oncologists may not yet have incorporated this into their practices, but this study further supports integrated boost with HF whole breast treatment as a standard of care option, Corbin says. “Potential benefits include improved efficiency of care and reduced time on treatment for patients, who value care that minimizes disruption in the rest of their life. When we can offer an equivalent treatment more efficiently, it is a win for both provider and patient.”

She adds that because of the individualized nature of breast cancer radiotherapy, integrated boost with HF whole breast treatment is among several choices that could be considered a standard of care.

Among future uses of integrated boosts, Corbin said she suspects they will be seen in the setting of women who are undergoing regional nodal irradiation. While this wasn’t allowed in the HYPOSIB trial, it was allowed in IMPORT HIGH, she noted.

Krug receivedgrant/research funding from Merck KGaA and Deutsche Krebshilfe; travel expenses from med update and ESMO; and compensation/ payment from Merck Sharp & Dohme, Pfizer, Onkowissen, med update, Gilead, ESO, ESMO, Astra Zeneca, and best practice onkologie. Three of the other authors reported disclosures. 

Corbin reported no relevant disclosures. 

Marcia Frellick is a freelance journalist based in Chicago. She has previously written for the Chicago Tribune, Science News, Northwestern magazine, and Nurse.com and was an editor at the Chicago Sun-Times, The Cincinnati Enquirer, and St. Cloud Times. Follow her on X:@MLfrellick