Pathological Changes Following Neoadjuvant Endocrine Therapy (NAET): A Multicentre Study of 391 Breast Cancers

Area of Science:

• Oncology
• Endocrinology
• Pathology

Background:

• Oestrogen receptor (ER)-positive breast cancer (BC) is typically responsive to endocrine therapy.
• Neoadjuvant endocrine therapy (NAET) is increasingly used for downstaging ER-positive tumours.
• Understanding NAET's impact on tumour characteristics is vital for optimizing treatment strategies.

Purpose of the Study:

• To analyze the effects of NAET on ER-positive breast cancer, focusing on morphological and biomarker expression changes.
• To evaluate treatment response and survival rates in patients undergoing NAET.
• To assess changes in hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) status post-NAET.

Main Methods:

• Retrospective analysis of 391 UK patients receiving NAET (Oct 2012 - Oct 2020).
• Detailed examination of paired pre- and post-NAET biopsies for morphological changes and receptor expression (ER, PR, HER2).
• Statistical analysis of treatment duration, survival rates, and biomarker conversions.

Main Results:

• 90.3% achieved pathological partial response, with higher response rates in HER2-low cancers.
• NAET induced stromal changes, increased tumour-infiltrating lymphocytes (TILs), and altered tumour cell morphology.
• Significant downgrading of tumour grade (19.3%) and conversion of PR (31.3%) and HER2 (38.1%) to negative status observed (p < 0.001).

Conclusions:

• NAET induces significant morphological and biomarker alterations in ER-positive breast cancer.
• Biomarker status (PR, HER2) can change following NAET, necessitating re-evaluation.
• Biomarker testing on both pre-treatment biopsies and post-treatment residual carcinoma is recommended.