Short-course preoperative endocrine therapy response acts as a functional test for hormone-sensitive breast cancer. Clinicians increasingly use this brief window to evaluate how a tumor reacts before definitive surgery. This approach helps tailor subsequent management for individual patients. Research highlights significant changes in tumor morphology after brief exposure to endocrine agents. Most notably, the mitotic count decreases dramatically during this period.

Factors Influencing Preoperative Endocrine Therapy Response

In a recent retrospective study, nearly 74% of patients achieved a Ki67 level of 10% or less after treatment. This reduction serves as a primary indicator of treatment success. Conversely, patients who underwent primary surgery without therapy showed no such decline in proliferation markers. These findings suggest that even a median duration of 29 days triggers measurable biological changes.

Furthermore, the MammaPrint assay provides valuable genomic insights into these outcomes. Patients with low-risk genomic profiles are much more likely to respond favorably to endocrine agents. Additionally, high baseline progesterone receptor levels correlate with improved sensitivity. Interestingly, while epithelial cells change, stromal elements like tumor-infiltrating lymphocytes remain stable. Consequently, the primary focus of response monitoring remains on the epithelial component. These insights assist surgeons and oncologists in refining personalized treatment plans for early-stage breast cancer.

How does Ki67 reflect endocrine sensitivity?

A decrease in Ki67 levels after endocrine therapy indicates that the treatment effectively inhibits cancer cell division. Specifically, a post-treatment Ki67 level of 10% or less suggests high sensitivity to hormone-based treatments.

What role does MammaPrint play in predicting treatment response?

The MammaPrint assay identifies the genomic risk of a tumor. Studies show that tumors with a low-risk genomic profile are significantly more likely to achieve a robust endocrine response compared to high-risk cases.

Disclaimer: This content is for informational and educational purposes only. It does not constitute medical advice or a substitute for professional healthcare consultations. Refer to the latest local and national guidelines for clinical practice.

References

Grosse C et al. Effects of short-course preoperative endocrine therapy on tumour morphology and immunohistochemical profile in oestrogen receptor-positive, HER2-negative breast cancer. Histopathology. 2026 Jun 18. doi: 10.1111/his.70203. PMID: 42315983.

Cleveland Clinic. Ki67 Protein Levels Predict Which Breast Cancer Patients Respond to Endocrine Therapy. Journal of Clinical Oncology. 2017.

Nardin S et al. Role of endocrine therapy in early-stage HR-positive breast cancer. ESMO Breast Cancer Annual Congress. 2024.