News > Tamoxifen Use Affected by Fertility Concerns, Side Effects

Tamoxifen Use Affected by Fertility Concerns, Side Effects


Study looks at why young women don’t start treatment or cut it short

The potential side effects and fertility impact of tamoxifen lead some young women to stop, or never start, the treatment despite its ability to help prevent cancer from coming back, a study shows.


Tamoxifen is a hormonal therapy given after treatment for hormone receptor-positive breast cancer. It reduces the risk of recurrence, the return of cancer. In the past, tamoxifen was taken for 5 years after primary treatment ended. Now, research shows that up to 10 years of tamoxifen further reduces the chance of breast cancer coming back.

Yet many women stop taking tamoxifen before they are supposed to, and some never start taking it at all. Young women are especially likely to do this.

The side effects of tamoxifen include hot flashes, mood disturbances and irregular periods. In rare cases it can cause endometrial (uterine) cancer, although premenopausal women have not been found to be at greater risk of developing it.

Women are advised not to become pregnant while taking tamoxifen because it can harm a fetus. Tamoxifen is not believed to directly affect fertility, but waiting 5 to 10 years to take a full course before becoming pregnant can impact fertility.

The researchers of this study wanted to find out if fertility concerns were related to young women’s decisions to stop, or never start, tamoxifen. They also wanted to know if other factors were involved.


The study enrolled women younger than age 45 and diagnosed with early-stage breast cancer treated at a Chicago hospital from 2007 to 2012. They were premenopausal and recommended for tamoxifen treatment.

Medical record review was used to determine the length of tamoxifen treatment for each woman and her reasons for not starting the medicine or for stopping before completing 5 years. Those who stopped or did not start were interviewed by phone to find out more about their decision.


Participants included 515 women, ages 25 to 45. In that group:

  • 71.1 percent started and stayed on tamoxifen for 5 years
  • 13.4 percent did not start
  • 15.5 percent stopped before completing 5 years

Of those who never started tamoxifen or delayed starting it:

  • 34 percent said they planned to become pregnant
  • 36 percent said they were concerned about possible side effects in general
  • 13 percent said they thought it would be of little benefit
  • 16 percent declined or had other reasons

Of those who stopped before completing 5 years:

  • 25 percent said they wanted to attempt pregnancy, or got pregnant while on tamoxifen
  • 63 percent said they were affected by side effects, especially mood changes, hot flashes, irregular periods and weight gain

Being diagnosed with DCIS, or stage 0 breast cancer, also predicted a woman would stop taking tamoxifen or not start at all. Only 58 percent started, compared with 93 percent of women with invasive disease. Women who smoked or who chose not to have radiation therapy were also more likely to stop taking tamoxifen early.

The researchers believe making fertility preservation a priority would improve tamoxifen use. They also believe more women would take tamoxifen if healthcare providers gave better information about personal recurrence risk, the medicine’s benefits and actual risk of uterine cancer.

What this means for you

Fertility and side effects are important to many young women. Talk with your doctor about your risk of breast cancer recurrence, your thoughts about becoming pregnant in the future and about tamoxifen use if you are concerned.

You might also want to talk about the possibility of timing tamoxifen treatment to try for a pregnancy. Some women take tamoxifen for a period of time, then stop temporarily to become pregnant. They are encouraged to complete tamoxifen therapy after giving birth.

An international study is looking at whether taking a break from tamoxifen in order to try for a pregnancy, then resuming treatment, has the same benefits as continuous therapy. The trial is open in the US. Learn more here.


Llarena NC, Estevez, SL, Tucker, SL, Jeruss, JS. Impact of Fertility Concerns on Tamoxifen Initiation and Persistence. Journal of the National Cancer Institute. 2015; doi: 10.1093/jnci/djv202

Accompanying Editorial: Rosenberg S, Partridge, A. New Insights Into Nonadherance With Adjuvant Endocrine Therapy Among Young Women With Breast Cancer. Journal of the National Cancer Institute. 2015; doi: 10.1093/jnci/djv202


This article was supported by the Grant or Cooperative Agreement Number 1 U58 DP005403, funded by the Centers for Disease Control and Prevention. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention or the Department of Health and Human Services.


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