- Design
- Retrospective single-centre cohort with paired biopsy and resection
- Population
- 180 women given short-course preoperative endocrine therapy vs 151 untreated controls
- Primary outcome
- Morphological and immunophenotypic change; Ki67 ≤10% response
- Effect
- Ki67 ≤10% in 73.9% vs 0%; grade fell in 36.7% vs 7.9%
Short-course preoperative endocrine therapy is increasingly used in ER-positive, HER2-negative breast cancer to test endocrine sensitivity. This retrospective single-centre study, published in June, compared paired biopsy and resection specimens from 180 treated women (median 29 days of therapy) with 151 women who went straight to surgery.
Ki67 fell to 10% or below in 73.9% of treated tumours and none of the controls. Histological grade fell in 36.7% of treated tumours against 7.9% of controls, mostly through lower mitotic counts. ER stayed stable, PR fell more often after treatment, and HER2-low status became more frequent. High genomic risk on MammaPrint and loss of PR were associated with failure to reach Ki67 of 10% or below.
For the reporting pathologist, this means the resection grade and Ki67 after endocrine therapy describe a treated tumour, not the untreated one. HER2-low calls can shift too, which matters now that HER2-low status affects eligibility for some therapies.
These are observational data from one centre; they describe what changes, not which values should guide treatment.
- Ask whether preoperative endocrine therapy was given before grading a breast resection.
- Expect lower mitotic counts and Ki67 after a month of treatment; grade may fall by one tier.
- State in the report that grade and Ki67 reflect post-treatment tissue.
- Reassess PR and HER2 on the resection; PR loss and HER2-low shifts were common.
- Keep the pretreatment biopsy values in view when the oncologist reads the report.
Why it matters
A resection report that does not mention prior endocrine therapy can understate the original tumour's grade to the team planning adjuvant treatment.
Don't overread it
This retrospective study shows what changes after therapy, not which post-treatment values should drive decisions.
The statistics, in plain English
A grade change in 36.7% of treated tumours against 7.9% of controls is a large difference. But the groups were not randomised, so other differences between them may contribute.
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