Taking low-dose tamoxifen daily for 3 years reduces the risk of breast cancer among patients with breast intraepithelial neoplasia, according to trial results published in the Journal of Clinical Oncology.

The phase 3 trial showed a reduced risk of invasive breast cancer and ductal carcinoma in situ (DCIS) that persisted 7 years after patients stopped taking tamoxifen.

The trial (TAM-01; ClinicalTrials.gov Identifier: NCT01357772) included 500 women with breast intraepithelial neoplasia, including atypical ductal hyperplasia (20%), lobular carcinoma in situ (LCIS; 11%), and hormone-sensitive or unknown DCIS (69%). 

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After undergoing surgery, with or without radiation, the patients were randomly assigned to receive tamoxifen at 5 mg daily (n=253) or placebo (n=247) for 3 years. 

At a median follow-up of 9.7 years, there were a total of 66 breast cancer diagnoses, including 51 cases of invasive breast cancer and 15 cases of DCIS. 

There were fewer breast cancers in the tamoxifen arm than in the placebo arm — 25 and 41, respectively (hazard ratio [HR], 0.58; 95% CI, 0.35-0.95; P =.03). 

There were fewer contralateral breast cancer events in the tamoxifen arm than in the placebo arm as well — 6 and 16, respectively (HR, 0.36; 95% CI, 0.14-0.92; P =.025).

Among patients with DCIS, there was a 50% reduction in the risk of recurrence with tamoxifen (HR, 0.50; 95% CI, 0.28-0.91; P =.02). 

The researchers calculated that 22 patients would need to be treated with tamoxifen to prevent 1 case of breast cancer in 5 years, and 14 patients would need to be treated to prevent 1 case in 10 years. 

There were 35 serious adverse events in the tamoxifen arm and 22 in the placebo arm. There was no significant difference in the number of non-breast cancers between the arms, and there were no treatment-related deaths in either arm.

“[O]ur findings provide strong support for the use of low-dose tamoxifen after a diagnosis of noninvasive neoplasia and open the door for new studies in the primary prevention of breast cancer in high-risk women,” the researchers concluded. 

Disclosures: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.


Lazzeroni M, Puntoni M, Guerrieri-Gonzaga A, et al. Randomized placebo controlled trial of low-dose tamoxifen to prevent recurrence in breast noninvasive neoplasia: A 10-year follow-up of TAM-01 study. J Clin Oncol. Published online March 14, 2023. doi:10.1200/JCO.22.02900