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Tamoxifen-Related Cancer in Early Stage Breast Cancer

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However, concerns have been raised that the drug (tamoxifen) may increase the incidence of new primary malignancies, such as endometrial, liver, and colorectal cancers.”

You’ve been diagnosed with either DCIS (BC stage 0) 0r early stage breast cancer. Your oncologist has recommended tamoxifen. No big deal. You’ve heard of this therapy. You know of other women who have undergone tamoxifen therapy.

Adjuvant tamoxifen therapy can reduce a woman’s risk of breast cancer relapse in the same breast. This much we know. But, according to the studies linked and excerpted below, adjuvant tamoxifen in early breast cancer patients causes “a nearly sixfold increase in endometrial cancers and a threefold increase in gastrointestinal cancers…”

So the question to consider is the risk/reward ratio of adjuvant tamoxifen therapy. Are there evidence-based non-toxic therapies that also reduce the risk of BC relapse?

Consider two possible therapy plans- 

  • Breast-conserving surgery aka lumpectomy and evidence-based, non-toxic therapies discussed in the DCIS guide. 
  • Breast-conserving surgery aka lumpectomy, low-dose tamoxifen (linked below), plus the evidence-based, non-toxic therapies in the DCIS guide. 

Look. I cannot presume to suggest how you want to treat your body. However, I don’t think that conventional oncology does a thorough job of explaining your options.

Scroll down the page and post a question or a comment. I will reply to you ASAP. Also, please download the DCIS guide linked in the banner above.

Hang in there,

David Emerson

  • Cancer Survivor
  • Cancer Coach
  • Director PeopleBeatingCancer

Recommended Reading:

Adjuvant Tamoxifen Therapy for Early Stage Breast Cancer and Second Primary Malignancies

“Background: Tamoxifen is being increasingly used for the treatment of breast cancer and is undergoing study for the primary prevention of breast cancer. However, concerns have been raised that the drug may increase the incidence of new primary malignancies, such as endometrial, liver, and colorectal cancers.
Purpose: Our goal was to assess the carcinogenic risks associated with long-term use of tamoxifen in women with early stage breast cancer.
Methods: The incidence of new primary cancers among 2729 women participants of the Stockholm Trial was determined at a median follow-up of 9 years. In this trial, after primary surgery, postmenopausal patients aged less than 71 years with unilateral invasive breast cancer were randomly allocated to receive either 2 years of adjuvant tamoxifen (40 mg daily) or no adjuvant endocrine therapy.
Information on second cancers was obtained by retrospective linkage to the Swedish Cancer Registry. To increase statistical power, a joint analysis of the incidence of endometrial and gastrointestinal cancers was performed in the following three major studies in Scandinavia evaluating adjuvant tamoxifen therapy: the Stockholm Trial, the Danish Breast Cancer Group Trial, and the South-Swedish Trial. These studies included a total of 4914 patients with a median follow-up of 8–9 years. All P values were calculated from two-tailed tests of statistical significance.
Results: In the Stockholm Trial, there was a statistically significant (P =.008) reduction in the incidence of second primary cancers in the contralateral breast among the tamoxifen-treated patients. However, there was a nearly sixfold increase in endometrial cancers and a threefold increase in gastrointestinal cancers in the tamoxifen-treated patients. The results of the joint studies showed a statistically significant increase in endometrial cancers among the tamoxifen-treated patients…
There was also an excess of gastrointestinal cancers associated with tamoxifen. Most of this excess involved colorectal cancers and stomach cancer…
There was no substantial increase in any other type of gastrointestinal cancer (e.g., liver cancer) among the tamoxifen-treated patients.
Conclusion: The endometrium and gastrointestinal organs may be target sites for tamoxifen-induced carcinogenesis in humans.
Implications: The increased incidence of colorectal and stomach cancers reported here should be regarded as tentative until supported by long-term data from a larger number of tamoxifen trials. Also, appropriate surveillance of cancer incidence is warranted for the protection of participants enrolled in current tamoxifen chemoprevention trials. [J Natl Cancer Inst 87: 645–651, 1995]

Tamoxifen and secondary tumours. An update 1997 Feb;16(2):104-17.

“In women treated with adjuvant tamoxifen the incidence of new primary breast cancers is decreased. This latter observation has led to the initiation of prevention trials. In 1989 the first report from a large prospective randomised trial showed a significant increase of endometrial carcinoma among women treated with adjuvant tamoxifen…

Randomized Placebo Controlled Trial of Low-Dose Tamoxifen to Prevent Local and Contralateral Recurrence in Breast Intraepithelial Neoplasia

“PURPOSE- Tamoxifen administered for 5 years at 20 mg/d is effective in breast cancer treatment and prevention, but toxicity has limited its broad use. Biomarker trials showed that 5 mg/d is not inferior to 20 mg/d in decreasing breast cancer proliferation. We hypothesized that a lower dose given for a shorter period could be as effective in preventing recurrence from breast intraepithelial neoplasia but have a lower toxicity than the standard dose.

PATIENTS AND METHODS-We conducted a multicenter randomized trial of tamoxifen, 5 mg/d or placebo administered for 3 years after surgery in women with hormone-sensitive or unknown breast intraepithelial neoplasia, including atypical ductal hyperplasia and lobular or ductal carcinoma in situ. The primary end point was the incidence of invasive breast cancer or ductal carcinoma in situ.

RESULTS-Five hundred women 75 years of age or younger were included. After a median follow-up of 5.1 years (interquartile range, 3.9-6.3 years), there were 14 neoplastic events with tamoxifen and 28 with placebo (11.6 v 23.9 per 1,000 person-years; hazard ratio, 0.48; 95% CI, 0.26 to 0.92; P = .02), which resulted in a 5-year number needed to treat of 22 (95% CI, 20 to 27). Tamoxifen decreased contralateral breast events by 75% (three v 12 events; hazard ratio, 0.25; 95% CI, 0.07 to 0.88; P = .02). Patient-reported outcomes were not different between arms except for a slight increase in frequency of daily hot flashes with tamoxifen (P = .02). There were 12 serious adverse events with tamoxifen and 16 with placebo, including one deep vein thrombosis and one stage I endometrial cancer with tamoxifen and one pulmonary embolism with placebo.

CONCLUSION-Tamoxifen at 5 mg/d for 3 years can halve the recurrence of breast intraepithelial neoplasia with a limited toxicity, which provides a new treatment option in these disorders…”


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