Aromatase Inhibitors for DCIS

The NSABP B35 trial:
- Was a phase 3 clinical trial that randomized postmenopausal women with ER+ DCIS (n = 3,104) to either 5 years of anastrozole or tamoxifen following breast-conserving surgery and radiation
- The trial sought to determine how effective anastrozole was compared to tamoxifen in preventing a breast cancer occurrence
- With a median follow-up of 9 years:
  - Investigators found significantly fewer breast cancer events in the anastrozole group (n = 90) than in the tamoxifen group (n = 122)
- The 10-year breast cancer event rate was lower among women randomized to anastrozole compared to tamoxifen:
  - 6.9% [anastrozole] vs. 10.9% [tamoxifen], HR 0.73, p=0.02:
    - This recorded difference in breast cancer events was attributable almost entirely to younger postmenopausal women less than 60 years of age who received tamoxifen:
      - Women less than 60 receiving tamoxifen had nearly twice the events as those receiving anastrozole:
        
        Events on tamoxifen: 63 vs events on anastrozole: 34, HR 0.53 (0.35-0.80), p=0.0026
    - Interestingly, the difference between treatments did not become apparent until after 5 years of follow-up, likely due to the low number of events in both groups
  - There was no difference in overall survival (OS) between the two treatment groups:
    - The 10-year estimates for overall survival were 92.1% for the tamoxifen group and 92.5% for the anastrozole group (p=0.38)
In B-35, anastrozole was found to further significantly reduce the rate of contralateral invasive cancer compared with tamoxifen
Based on this trial and others:
- Aromatase inhibitors are the preferred adjuvant hormonal therapy for ER+ disease in post-menopausal women with either DCIS or invasive breast cancer, provided they have no contraindications to taking an aromatase inhibitor
References
- Margolese RG, Cecchini RS, Julian TB, Ganz PA, Constantino JP, Vallow LA, et al. Anastrozole versus tamoxifen in postmenopausal women with ductal carcinoma in situ undergoing lumpectomy plus radiotherapy (NSABP B-35): a randomised, double-blind, phase 3 clinical trial. Lancet. 2016;387(10021):849-856
- M Baum, AU Budzar, J Cuzick, et al., ATAC Trialists’ Group. Anastrozole alone or in combination with tamoxifen versus tamoxifen alone for adjuvant treatment of postmenopausal women with early breast cancer: first results of the ATAC randomized trial. Lancet. 2002;359(9324):2131-2139.