I think the reason the UK is running the POSNOC trial is because the USA ran a similar one (in (2011) and their methods are changing due to this. It is now standard in the USA not to routinely remove lymph nodes if one is found with cancer and the patient is having the appropriate chemo, rads etc.
My surgery was in November and I was faced with a similar decision but the other way around.
As my lump was large and in a difficult place my Oncologist suggested on diagnosis, that I start with chemo and then have a lumpectomy if it shrank enough. I also had a lymph node positive.
The chemo really did the trick for me. My lump shrunk away to almost nothing and so I decided to have a Lymph node biopsy rather than a removal. There was no cancer found in the nodes in the end.
Partly, I made that decision based on the USA research that showed for women with one positive lymph node the survival rate was about the same as woman with no node involvement, who had chemo and rads (i.e. I didn’t need my lymph nodes removed).
Here’s a snip from about the USA research in 2011 (similar to POSNOC)
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Subsequently, the American College of Surgeons Oncology Group, which is another NCI clinical trials cooperative group, reported findings from an additional phase III clinical trial, this one testing whether women with a positive sentinel lymph node but no clinical evidence of axillary lymph node metastasis could be safely treated with tumor removal and no further lymph node surgery other than the SLNB (3). In this trial, 891 women were randomly assigned to SLNB only or ALND after SLNB (3). All of the women were treated with lumpectomy. More than 95 percent of them also received adjuvant systemic therapy (chemotherapy, hormone therapy, or both), and about 90 percent received external-beam radiation therapy to the affected breast.
When the results of this trial were reported, the patients had been followed for a median of 6.3 years. The two groups of women had similar 5-year overall survival (92.5 percent in the SLNB-only group versus 91.8 percent in the SLNB plus ALND group) and 5-year disease-free survival (83.9 percent in the SLNB-only group and 82.2 percent in the SLNB plus ALND group). The researchers concluded that SLNB alone is safe and does not affect the survival of women who have sentinel lymph node metastasis but no clinical signs of other lymph node involvement and whose breast cancer is treated with surgery, systemic therapy, and external-beam radiation therapy. The excellent outcome in this trial for women treated with SLNB without ALND is likely due, at least in part, to the ability of local radiation therapy and modern systemic treatments to effectively treat breast cancer cells that may have spread to other axillary lymph nodes besides the sentinel node or to other parts of the body.
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cancer.gov/about-cancer/diagnosis-staging/staging/sentinel-node-biopsy-fact-sheet