Background
Tamoxifen 20 mg daily for 5 years reduces the risk of breast cancer by 49% in women with family history, and up to 85% in women with history of atypical ductal (ADH) or lobular hyperplasia (ALH) (NSABP-P1). In 2019, the TAM-01 trial demonstrated 50% reduction using a 5 mg daily dose for 3 years (TAM-01). Small studies have suggested higher uptake of this lower dose option (Mayo low-dose tam study). We aim to evaluate real-world uptake, adherence and efficacy.
Methods
A retrospective chart review was performed evaluating patients seen in the Mayo Clinic Breast Clinic between January 2019 and December 2021 with diagnosis of ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS), ADH, ALH, or elevated lifetime risk of breast cancer and were recommended Tamoxifen. Comparison was made between 20 mg daily, 10 mg every other day, and no Tamoxifen arms. Primary outcomes were completion of Tamoxifen course and new cancer events (recurrent or new contralateral malignancies).
Conclusions
Completion rates between full-dose and low-dose Tamoxifen were similar between the two groups. We noted that women in the full-dose group were significantly younger, indicating a higher comfort in full-dose with highest risk women. Rates of adverse events were similar, but we were not able to evaluate severity of symptoms in this retrospective review. We noted a higher rate of new or recurrent malignancies with the low-dose Tam group although not statistically significant. Longer follow-up and a prospective study design in a real-world setting will be important going forward.