Skip to main content
SSO 2024 Annual Meeting Main banner
Icon Legend
This session is not in your schedule.
This session is in your schedule. Click again to remove it.
Presentation Icons
Recorded for On-Demand Viewing
Recorded for On-Demand Viewing
Back

Breast

E11: Effect of tamoxifen on proliferation of background normal lobules in breast disease.

Introduction:

Tamoxifen (Tam) is an effective chemopreventive agent that reduces risk of estrogen receptor (ER) positive breast cancer (BC) risk by 50%. However, concerns about side effects have limited its uptake, and biomarkers to predict benefit are lacking. Thus, we analyzed changes in the proliferation marker Ki67 in normal lobules of biopsies in relation to tamoxifen treatment.

Methods:

Women with benign breast disease (BBD) or BC (stage 0-III) from 1995 to 2020 with paired pre-tamoxifen (PreTam) and on-tamoxifen (OnTam) breast tissue samples with normal lobules were evaluated retrospectively. Exclusion factors included chemotherapy, prior radiation, PreTam sample >1 year prior to Tam start, or OnTam sample < 1 month after Tam start. Percent of Ki67 expressing cells were quantified in up to 10 normal lobules per sample with Aperio software; the median Ki67% across lobules within biopsy was calculated and used for analysis. The change in normal lobule Ki67 between paired PreTam and OnTam samples per patient was assessed with Wilcoxon signed-rank test.

Results:

To date, we have evaluated 24 women (median age at PreTam biopsy = 50 years, median BMI = 25.2 kg/m2) with a median interval of 9 months between biopsies; OnTam samples were obtained at median 6 months after the start of Tam. Tam dose per day was 20 mg in 83%, 10 mg in 17%, and unknown in 1.  Per-biopsy median Ki67 values ranged from 0-6.9% PreTam (median 0.7%) and from 0-4.8% OnTam (median 0.6%) with no significant change overall (p=0.36). Assessed by PreTam starting Ki67 value, among 37.5% (9/24) samples with Ki67 levels < 0.5%, no decrease in Ki67 was found in OnTam samples. Conversely, among 62.5% (15/24) with PreTam Ki67 ≥ 0.5%, the OnTam samples showed significant Ki67 reductions [median change -0.5 (range: -6.7 to +3.5), p=0.03] (Fig 1).

Conclusions:

We observed significant Ki67 reductions in normal breast lobules with Tam use among women with baseline Ki67≥0.5%, suggesting the potential to use change in Ki67 as a biomarker to assess response among these women.

Learning Objectives:

  • Upon completion, participant will be able to understand the rationale for Ki67 as a biomarker of proliferation in normal breast lobules.
  • Upon completion, participant will be able to explain that tamoxifen therapy induces Ki67 reduction in normal lobules only when baseline Ki67 is elevated.
  • Upon completion, participant will be able to describe the potential utility of Ki67 change as a biomarker of tamoxifen response.