A radiation regimen with fewer but larger fractions appears to be as effective as the conventional regimen of 25 fractions in reducing risk for recurrence of early breast cancer, according to results of a phase III study presented at the annual meeting of the American Society of Clinical Oncology.

The study is the largest to date to study hypofractionation of postoperative radiation therapy in patients with early breast cancer.

“These findings suggest that women can safely undergo a less demanding course of radiation therapy without appearing to increase their risk of recurrence,” said John A. Dewar, MD, clinical oncologist at the University of Dundee, UK, and a coauthor of the START (Standardisation of Breast Radiotherapy) Trial.

Previous study had suggested that breast cancer may be more responsive to modest increases in fraction size than originally thought. Thus, physicians hypothesized that reductions in the overall radiation dose and treatment period could be possible without jeopardizing either effectiveness or safety of therapy.

The START trial was made up of two concurrently conducted studies. In the first (ST-A), 2236 women who had already undergone surgery were randomized to receive either 50 Gy in 25 fractions over five weeks or doses of 39 or 41.6 Gy in 13 fractions over five weeks. In ST-B, 2215 patients received either 50 Gy in 25 fractions over five weeks or 40 Gy given in 15 fractions over three weeks.

The incidence of locally recurrent tumor and the effects of treatment on nearby, healthy breast tissue were compared among different groups, with detailed photographic assessments in 44 percent of patients.

After median follow-up of 5.1 years (ST-A) or 6.0 years (ST-B), the incidence of local recurrence was very low in all groups. In ST-A, estimated five-year recurrence for the 50 Gy group was 3.6 percent compared with 3.5 percent for the 41 Gy group and 5.2 percent for the 39 Gy group. In ST-B, estimated five-year local recurrence rate was 3.3 percent for the 50 Gy group and 2.2 percent for the 40 Gy group.

Because the numbers of patients with recurrence were so low, investigators noted that it was not possible to determine definitively whether recurrence rates among women receiving hypofractionated therapy would change with time.

Among patients in ST-A who received detailed assessment, the proportion with a negative change in breast appearance at five years was 32 percent for the 39 Gy group, 43 percent in the 50 Gy group, and 44 percent in the 41.6 Gy group. In ST-B, proportions were 36 percent for 40 Gy and 42 percent for 50 Gy.

In ST-A, the rate for moderate or marked breast shrinkage, edema, telangiectasia, or induration was lower for the 39 Gy group than for the 50 Gy group. In ST-B, the rate of moderate or severe edema and telangiectasia were lower for 40 Gy than for 50 Gy.