Basically what I did was present the results of a phase III trial comparing partial breast irradiation versus whole breast irradiation for the NRG oncology group. Basically what we did was to look at 4,216 women, we randomised half of them to whole breast irradiation performed over 5-7 weeks, the traditional standard of care, versus partial breast irradiation using one of three partial breast irradiation techniques – either 3D conformal external beam radiation therapy, interstitial brachytherapy or device-based brachytherapy. Patients were stratified, stratification factors of menopausal status, disease stage, a few other things. Then what we did was to follow these patients over ten years and the primary endpoint was ipsilateral breast tumour recurrence, in other words recurrence of the cancer in the lumpectomy bed area.

It was an equivalence test so what it was designed to do was to determine whether or not partial breast produced the same results in terms of ipsilateral breast tumour recurrence. Unfortunately, the results we did not quite meet equivalence but the difference was only 0.7%. So statistically we did not demonstrate equivalence but the difference at ten years was very, very small. We also looked at what’s called relapse free interval which is the time from randomisation to the development of a first local, regional or distant recurrence, regardless of an intervening second cancer or contralateral breast cancer. What we saw was that at ten years there was a 1.6% difference between partial and whole breast irradiation that was statistically significant. Again, it was a very small difference but it was statistically significant. We also looked at disease free survival, overall survival, distant metastasis free interval etc., those were all not statistically significant so, in other words, did not impact on cure rates, things like that.

So our conclusions were that, yes, we did not demonstrate equivalence based upon the upper limit of the confidence interval for the hazard ratio, that’s the statistical interpretation, but that difference was less than 1% at ten years. The same thing with the relapse free interval – there was a slight difference that was statistically significant but still they were not proven to be equal. We looked at other things such as toxicities and second cancers, we did not find any difference between the two. But our conclusions were that for a large proportion of women partial breast irradiation is an acceptable alternative to whole breast irradiation. And indeed that is the case, there are many parts of the country that have been doing partial breast irradiation for the last decade.

So the strengths of this study were it was the largest partial breast irradiation study; the eligibility criteria were quite diverse – we included patients with positive lymph nodes, younger patients, ductal carcinoma in situ. We really wanted to know exactly are there differences at ten years because this has been used for quite some time. So the power of the study is, yes, it did show that there was a slight difference that didn’t quite meet statistical equivalence but, nonetheless, reassuring us that applied in the right groups of patients this is very safe and does help women who want to improve their quality of life and not go through an extensive period of radiation therapy.