Partial breast irradiation for early breast cancer

Breast conserving therapy for women with breast cancer consists of local excision of the tumour (achieving clear margins) followed by radiation therapy (RT). RT is given to sterilize tumour cells that may remain after surgery to decrease the risk of local tumour recurrence. Most true recurrences occur in the same quadrant as the original tumour. Whole breast RT may not protect against the development of a new primary cancer developing in other quadrants of the breast. In this Cochrane Review, we investigated the role of delivering radiation to a limited volume of the breast around the tumour bed (partial breast irradiation: PBI) sometimes with a shortened treatment duration (accelerated partial breast irradiation: APBI).

To determine whether PBI/APBI is equivalent to or better than conventional or hypofractionated WBRT after breast conservation therapy for early-stage breast cancer.

We searched the Cochrane Breast Cancer Group Specialised Register (07 November 2013), CENTRAL (2014, Issue 3), MEDLINE (January 1966 to 11 April 2014), EMBASE (1980 to 11 April 2014), CINAHL (11 April 2014) and Current Contents (11 April 2014). Also we searched the International Standard Randomised Controlled Trial Number Register, the World Health Organization's International Clinical Trials Registry Platform (07 November 2013) and US clinical trials registry (www.clinicaltrials.gov) (22 April 2014). We searched for grey literature: Open Grey (23 April 2014), reference lists of articles, a number of conference proceedings and published abstracts, and did not apply any language restrictions.

Randomised controlled trials (RCTs) without confounding and evaluating conservative surgery plus PBI/APBI versus conservative surgery plus whole breast RT. We included both published and unpublished trials.

Three review authors (ML, DF and BH) performed data extraction and resolved any disagreements through discussion. We entered data into Review Manager for analysis. BH and ML assessed trials, graded the methodological quality using Cochrane's Risk of Bias tool and resolved any disagreements through discussion.

We included four RCTs that had 2253 women. Two older trials examined RT techniques which do not reflect current practice and one trial had a short follow-up. We downgraded the quality of the evidence for our key outcomes due to risk of bias. Taken together with other GRADE recommendations, the quality of evidence for our outcomes was very low to low. For the comparison of partial breast irradiation/accelerated breast irradiation (PBI/APBI) with whole breast irradiation (WBRT), local recurrence-free survival appeared worse (Hazard Ratio (HR) 1.74, 95% confidence interval (CI) 1.23 to 2.45; three trials, 1140 participants, very low quality evidence). Cosmesis appeared improved with PBI/APBI in a single trial (OR 0.40, 95% CI 0.23 to 0.72; one trial, 241 participants, very low quality evidence), but late toxicity (telangiectasia OR 4.41, 95% CI 3.21 to 6.05; very low quality evidence, 708 participants) and subcutaneous fibrosis (OR 4.27, 95% CI 3.04 to 6.01; one trial, 710 participants, very low quality evidence) appeared increased in another trial. We found no clear evidence of a difference for the comparison of PBI/APBI versus WBRT for the outcomes of: overall survival (HR 0.99, 95% CI 0.83 to 1.18; three trials, 1140 participants, very low quality evidence), cause-specific survival (HR 0.95, 95% CI 0.74 to 1.22; two trials, 966 participants, low evidence quality), distant metastasis-free survival (HR 1.02, 95% CI 0.81 to 1.28; 1140 participants, low quality evidence), subsequent mastectomy rate (OR 0.20, 95% CI 0.01 to 4.21; 258 participants, low quality evidence) and relapse-free survival (HR 0.99, 95% CI 0.53 to 1.85; 258 participants, low quality evidence). We found no data for the outcomes of acute toxicity, new ipsilateral breast primaries, costs, quality of life or consumer preference.

The limitations of the data currently available mean that we cannot make definitive conclusions about the efficacy and safety or ways to deliver of PBI/APBI. We await completion of ongoing trials.