Some interesting facts about Tamoxifen and breast cancer recurrence:

In 2009
211,731 women were diagnosed w/ BC
40,676 died

In 2011 (approx)
230,480 diagnosed
39,520 died

In 2012 (approx)
232,340 diagnosed
39,620 died

For any woman in the US, the chance of dying of BC is 1 in 36 (~4%)
For any woman in the US, the chance of getting BC is 12%

Stage 0 has a 93% chance of survival with surgery + chemo/radiation
Stage 1 has a 88% chance of survival with surgery + chemo/radiation

Back in 2011 a study was published in Lancet regarding long term tamoxifen efficacy. (Here’s a link to the full study.) The study included participants who had every type of tumor receptivity, and separated participants into groups according to the specific hormone receptivity of their tumors. The study counted any return of breast cancer, whether local or distant.  (Local means the same breast that originally had cancer, distant means that the cancer cells grew in a different part of the body. They can tells the difference by looking at the cancer cells under a microscope.)

In looking at the study, and focusing on the women with strongly ER positive breast cancer, the type that should benefit most from tamoxifen (and the kind I had), we find that this group included women with ER+ cancers, with and without PR+ receptivity, including 44% who had node positive breast cancer, 56% who did not, and 51% who received chemotherapy. Ultimately, those in the tamoxifen group took the drug for five years.

• For all ER+ women, there were in years 0-4, a rate of 3.74% who had recurrences among those who took tamoxifen, compared to a rate of 6.71% in the group that did not.  Which means that there were 2.97% fewer recurrences in the group that took tamoxifen, for a relative decrease of 44.2% in rate of recurrence with tamoxifen.
• For all ER+ women, in years 5-9, 2.62% had recurrences while taking tamoxifen compared to 3.46% among those who did not, a decrease of 0.84% in the number of recurrences with tamoxifen, and a relative decrease of 24.3% in the rate of recurrence.
• For years 0-4, for all node negative ER+ patients, the recurrence rate is 5.5 (there were 500 recurrences in over 9000 patients), which is low to start with. Tamoxifen reduced that to a rate of 250 recurrences in just under 10,000 patients, which is indeed an impressive reduction of 50%.
• This also means that 96.3% of women taking tamoxifen in years 0-4 did not have recurrences, and neither did 93.3% of the women who did not take it.
• In years 5-9, 97.4% of women taking tamoxifen did not have recurrences, and neither did 96.5% of the women who did not.
• ER+ women who took tamoxifen for 1-2 years had nearly as great a reduction in recurrence in years 0-4 as those who took it for it for five years.

But we’re talking about life and death here, so . . . is it worth the risk?

Again focusing on all women with strongly ER+ tumors, we see that b Breast cancer mortality was calculated by starting with the total death rate among all of the study participants, and subtracting the death rate for those women who never had a recurrence of breast cancer, who presumably died of other causes. All of these rates and percentages are technically projected, based on taking tamoxifen for five years, but the projections are based on the hard data of comparing mortality rates with recurrence rates.

• In years 0-4 after initial diagnosis of breast cancer, 1.79% of ER+ women taking tamoxifen died of breast cancer, compared to 2.46% of women who did not take tamoxifen and also died of breast cancer. This represents a difference of 0.67% in the number of breast cancer deaths between the two groups, or a decrease in the breast cancer mortality rate of 27.2% associated with taking tamoxifen in these years.
• In years 5-9, 2.25% of ER+ women who took tamoxifen for five years died of breast cancer, compared to 3.23% of women who did not take tamoxifen, for a difference of 0.98% in the number of breast cancer deaths between these two groups. The decrease in the rate of breast cancer mortality associated with five years of tamoxifen use was 30.3% in these years.
• In years 10-14, 1.54% of ER+ women who took tamoxifen for five years died of breast cancer, compared to 2.28% among those who did not take it. There were 0.74% more deaths by breast cancer in the latter group, and the decrease in the breast cancer mortality rate associated with five years of tamoxifen use was 32.5%.
• For ER+ women who were 15 years or more from their initial diagnosis, the mortality rate was 1.48% in the tamoxifen group, 1.89% in the control group, a difference of 0.41% in the number of breast cancer deaths, or a 21.7% relative decrease in mortality associated with five years of tamoxifen use.
• ER+ women who took tamoxifen for only 1-2 years experienced a continued decrease in mortality after five years from initial diagnosis.

The study also compared the rates of recurrence and mortality for women with ER+ tumors under age 45 at diagnosis, and those between 55 and 69 at diagnosis, and found comparable statistics. This analysis can be found in Figure 6. of the full study.