Arch Intern Med. 2006 May 8;166(9):1027-32

Chen WY, Manson JE, Hankinson SE, Rosner B, Holmes MD, Willett WC, Colditz GA.

BACKGROUND: Although short-term unopposed estrogen use does not seem to increase breast cancer risk, the effect of longer-term estrogen use remains unclear. We sought to assess the relationship between longer-term use of unopposed estrogen and the risk of invasive breast cancer over an extended follow-up period.

METHODS: Within the Nurses' Health Study, a prospective cohort study, we observed 11 508 postmenopausal women who had a hysterectomy and reported information on estrogen use at baseline (1980). The study population was expanded every 2 years to include women who subsequently became postmenopausal and had a hysterectomy, so that 28 835 women were included in the final follow-up period (2000-2002). Estrogen use was assessed from self-reported data on biennial questionnaires. The main outcome was invasive breast cancer.

RESULTS: A total of 934 invasive breast cancers were included in the analysis. Breast cancer risk increased with duration of unopposed estrogen use among longer-term users with the highest risk seen in cancers positive for estrogen receptor (ER+) and progesterone receptor (PR+). The multivariate relative risks (RRs) and 95% confidence intervals (CIs) for breast cancer with current use of unopposed estrogen for less than 5 years, 5 to 9.9 years, 10 to 14.9 years, 15 to 19.9 years, and 20 years or longer were, respectively, 0.96 (95% CI, 0.75-1.22), 0.90 (95% CI, 0.73-1.12), 1.06 (95% CI, 0.87-1.30), 1.18 (95% CI, 0.95-1.48), and 1.42 (95% CI, 1.13-1.77) (P for trend <.001). The risk of ER+/PR+ breast cancers was noted to be statistically significant after 15 years of current use (RR, 1.48; 95% CI, 1.05-2.07).

CONCLUSION: Users of unopposed estrogen were at increased risk of breast cancer but only after longer-term use.

Estudio de las Enfermeras.

Grupo de Histerectomizadas, tratadas con estrógenos solos.

Las usuarias de estrógenos conjugados equinos mostraron un aumento significativo en la incidencia de cáncer de mama, solo después de 20 años de uso ( RR 1,42 95% IC 1,13-1,77).

En el caso de los cánceres ER+ PR+, el RR fue de 1,49; 95%IC 1.05-2.07, en mas de 15 años de uso, pero dado por el grupo mayor de 20 años de uso, ya que el  RR  en el grupo 15 a 19,9 años fue de 1,18 sin significación estadística (95%IC 0,95 - 1,48).

Este trabajo indica que los plazos establecidos para limitar la duración de la terapia a cinco años no son aplicables a estrógenos solos, y solo deberían ser considerados para tratamientos con Estrógenos Conjugados Equinos + Medroxiprogestrona Acetato.

Adaptado de Chen WY, Manson JE, Hankinson SE, Rosner B, Holmes MD, Willett WC, Colditz GA.

Arch Intern Med. 2006 May 8;166(9):1027-32.