Low Dose Tamoxifen for Breast Cancer Prevention: A Real-World Experience

Purpose: There is limited data on the use of low dose tamoxifen (LDT) for chemoprevention since its introduction in 2019. This study sought to determine the rate of LDT uptake at our institution and describe factors associated with its use.

Methods: We performed a retrospective chart review of women diagnosed with ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS), and/or atypical hyperplasia from 2019 to 2021. Log-binomial models were used to compare the probabilities of receiving standard dose tamoxifen (SDT) relative to LDT by patient and disease characteristics. Since most patients did not experience any AEs, a zero-inflated poison regression model was used to estimate and compare adverse event rates between groups.

Results: Among 477 patients with DCIS, LCIS, and atypical hyperplasia, 27% (N = 129) initiated SDT, 19% (N = 89) LDT, 32% (N = 155) aromatase inhibitor, 2% (N = 9) raloxifene, and 20% (N = 95) declined therapy. LDT was used more frequently than SDT in patients with LCIS or atypical hyperplasia compared to DCIS (31.4% vs 17.4%, P < .0001). There were no significant differences in the frequency of adverse events between patients on SDT and LDT but the incidence rate of AEs in the SDT group was higher (1.9 vs. 1.3 per 1000 days, P = .0186).

Conclusion: In our population, 19% of women with DCIS, LCIS, or atypical hyperplasia, initiated chemoprevention with LDT with higher usage in patients with atypical lesions and/or LCIS. Physicians should strongly consider LDT in women with high-risk lesions who are eligible for chemoprevention.