The study I presented at San Antonio Breast Cancer Congress was about omission of the sentinel lymph node biopsy in early-stage breast cancer. We presented a five-year outcome, regional recurrence free survival. More specific, if you want to know some background, earlier studies showed that de-escalation concerning axillary treatment was safe concerning overall survival and what we learned more and more is that systemic therapy was more and more based on biology rather than nodal status. So more and more on biological subtype and grade. In early stage breast cancer most of the sentinel lymph nodes the pathology is without metastatic disease. So here we started with a study on omission of the sentinel lymph node biopsy in early-stage breast cancer. There are more studies like that, the SOUND and INSEMA, and they already presented their output at San Antonio last year and the year before and also in their studies omission of sentinel lymph node biopsy appeared safe.
The design of the Dutch BOOG study is women over 18 were included with unilateral early-stage breast cancer, clinically node negative, always confirmed with an ultrasound. Patients were randomised to one of the two study arms – arm A with the sentinel lymph node biopsy and arm B without. In arm A, in the sentinel lymph node biopsy, completion of axillary treatment, radiotherapy, axillary lymph node dissection, was allowed in the cases indicated. Systemic therapy was based on the information provided for both study arms.
If we have a look at patient characteristics we can see that the age is about 61 and almost 90% of the patients were above the age of 50. Most patients had a grade 1/2 tumour and most tumours were T1 stage. Almost all tumours were hormone receptor positive.
What is a significant finding is that systemic therapy is much lower compared to the previous sentinel lymph node omission studies because most patients didn’t receive systemic therapy. About 12% of patients received chemotherapy and 44% endocrine therapy. There is no significant treatment difference between treatment arms so medical oncologists did engage less but also not more systemic therapy to patients in the no sentinel lymph node biopsy arm.
If we have a look at the primary outcome then, regional recurrence free survival, the probability therefore there was 96.6% for patients in the sentinel lymph node biopsy and 94.2% for patients in the no sentinel lymph node biopsy. That’s after a median follow-up of five years, the absolute difference is 2.35% and with some complicated statistics we know that the upper boundary of the confidence interval is below the preset margin of 5% and that proves that it’s non-inferior. We also did an intention to treat analysis and that analysis had about the same outcome.
Concerning events, regional recurrence appeared in eight patients in the no sentinel lymph node arm and in three in the sentinel lymph node arm.
So what we finally concluded is the study examined omission of the sentinel lymph node biopsy in early-stage breast cancer and we found non-inferior results. Then we decided to perform a sub-analysis on the group which was advised for a no sentinel lymph node strategy by the authors of the SOUND and INSEMA studies. That meant patients with T1 tumours, ER+, grade 1/2 and above the age of 50 and that accounted in our study for 949 patients, about 60% of the whole patient population.
We made a really nice table with all kinds of events deduced from all three studies and then we can see in the table that the event rate and the percentage is about similar among these three studies. We think that this sub-analysis confirms the advice of the SOUND and INSEMA studies to omit the sentinel lymph node biopsy in this specific patient group – T1, ER+, grade 1/2, above the age of 50. For all other patients we think more mature data need to be awaited because they are much less represented in the whole study and we think a meta-analysis would be really of value for these patient groups.
What is really good to know is that in previous studies most patients had endocrine therapy, almost 100%, and in the Dutch study that only was 44%. So maybe it was previously suggested that endocrine therapy was a prerequisite for the omission of sentinel lymph node. I think we proved with this study that it is not.
A last thing which is really important to know is that Dutch radiotherapists really stick to the EORTC radiotherapy atlas and that meant that incidental radiotherapy to the axillary region was only found in 1.5% of the patients. That actually means that the Dutch BOOG 13-08 study is a really clean study where less surgery is not compensated with more endocrine therapy or more radiotherapy. For Monday morning in practice we advise to omit a sentinel lymph node in patients with T1, ER+ breast cancer grade 1/2 with patients who are above the age of 50.
