Tamoxifen can be used off-label to treat breast pain (mastalgia), because it reduces estrogen levels that cause breast swelling.In one study, tamoxifen relieved pain in more than two-thirds of women who had a history of severe breast pain. Experts disagree about the use of tamoxifen for breast pain, because it has important side effects and risks.
One double blind randomized comparatiove study(RCT) compared tamoxifen 20 mg daily versus placebo. It found that significantly more women experienced pain relief (measured by visual analogue scale over 3 months) with tamoxifen compared with placebo (> 50% reduction in mean pain score: 22/31 [71%] with tamoxifen v 11/29 [38%] with placebo; P < 0.025). The second RCT (93 women) compared tamoxifen, danazol, and placebo. It found that significantly more women taking tamoxifen achieved a good outcome (> 50% reduction in mean pain score) at the end of treatment, 6 months later, and 12 months later, compared with placebo (> 50% reduction in pain score after 6 months of treatment: 23/32 [72%] with tamoxifen v 11/29 [38%] with placebo; P = 0.035). The third RCT (88 women, aged 22–44 years) found that 8 months of tamoxifen increased the proportion of women who achieved complete recovery (outcome not clearly defined) compared with placebo (40/44 [90%] with tamoxifen v 0/44 [0%] with placebo; P value not reported).
In conclusion, Tamoxifen is not licensed for mastalgia in the UK or USA. There is a consensus to limit its use to no more than 6 months at a time under expert supervision, and with appropriate non-hormonal contraception, because of the high incidence of adverse effects.
Fentiman IS (2004). Management of breast pain. In JR Harris et al., eds., Diseases of the Breast, 3rd ed., pp. 57–62. Philadelphia: Lippincott Williams and Wilkins.
Kontostolis E, Stefanidis K, Navrozoglou I, et al. Comparison of tamoxifen with danazol for treatment of cyclical mastalgia. Gynecol Endocrinol 1997;11:393–397.
Fentiman IS, Caleffi M, Brame K, et al. Double-blind controlled trial of tamoxifen therapy for mastalgia. Lancet 1986;1:287–288.
Grio R, Cellura A, Geranio R, et al. Clinical efficacy of tamoxifen in the treatment of premenstrual mastodynia. Minerva Ginecol 1998;50:101–103. GEMB Group. Tamoxifen therapy for cyclical mastalgia: dose randomised trial. Breast 1997;5:212–213.