Gain vs. Pain: Is It Time To Switch Back To Tamoxifen?

Patient Expert

Are you a postmenopausal survivor taking an aromatase inhibitor to prevent a recurrence?

Whether you answer yes or no to the question above, keep reading. Because if you're a breast cancer survivor taking hormonal therapy (as about 80% of us are), this post applies to you: either now, or in the future.

If your breast cancer was hormone-receptive (shorthand in the pathology report: ER/PR+), and you've been treated within the past 8 to 10 years or so, it's a safe bet you've taken tamoxifen, and/or an aromatase inhibitor: Femara, Aromasin, or Arimidex. All of these drugs fight cancer recurrence by suppressing estrogen, in one way or another. Deprive hormone-receptive cancer cells of their estrogen, and they die or that's the goal, anyway.

For 30+ years, tamoxifen has been the gold standard for hormonal therapy. This drug, with its proven ability to lower recurrence risk with relatively slight side effects, has kept hundreds of thousands of women cancer-free.

But it's not 100% effective in all women; no drugs are. Researchers are constantly working to develop new drugs that provide better protection. And about 10 years ago a new class of drugs, called aromatase inhibitors, were introduced as the next best thing, the successor to tamoxifen.

It's true, AIs aren't for everyone; they're currently prescribed for hormone-receptive women with early stage cancer (cancer confined to the breast and lymph nodes) who've gone past menopause either naturally, or due to surgery or chemo. AIs won't work if your ovaries are still producing estrogen; but they work very well indeed if you meet the specific criteria for their use.

Over the past 5 years or so, there's been a gradual shift away from tamoxifen, and towards AIs. The speed of this shift has increased over the past year, due to two discoveries. First, it was found that some women aren't protected by tamoxifen as well as others; tamoxifen requires a certain human enzyme to be metabolized, and the reduced activity of that enzyme, CYP2D6, can prevent tamoxifen from doing its job

Second, the results of multiple clinical trials have shown that AIs are significantly more effective than tamoxifen at preventing recurrence again, for postmenopausal women with early-stage, hormone-receptive cancer. The ATAC trial (Arimidex vs. tamoxifen) and the BIG 1-98 trial (Femara and Aromasin) both show conclusively that AIs are the way to go with data now stretching out 6 to 7 years.

Unlike tamoxifen, AIs don't come with the risk of endometrial cancer another plus. But AIs do have two huge strikes against them. First, they absolutely cause a loss of bone mineral density. Read: they set you on the path to osteoporosis, with its inherent bone fractures.

And second, in some women they can produce joint pain so severe that it's impossible to stay the course.

How much gain for how much pain? That's what many of us have to ask ourselves. Is quality of life more important than a reduced risk of recurrence? Tough question; no good answer.

Now, results of a study presented at the San Antonio Breast Cancer Symposium last December might provide hope for women caught in this damned-if-you-do situation. If extended results of the BIG 1-98 trial, comparing Femara to tamoxifen, can be applied to all AIs, then relief may be on the way for anyone considering dropping their therapy due to pain.

It appears that taking Femara for 2 years, then switching to tamoxifen for the next 3 years, provides equal benefit to taking Femara for 5 years.

So" Does that mean that if you're in severe pain from Femara, you can quit taking it after 2 years and switch to tamoxifen without increasing your risk of recurrence? Or if you're at high risk for osteoporosis, you can switch to bone-building tamoxifen after 2 years of bone-destroying Femara and receive the same protection from recurrence?

Apparently so.

The picture isn't complete yet; researchers are continuing to study the long-range efficacy of both AIs and tamoxifen. And only Femara not Arimidex or Aromasin have been tested against tamoxifen in quite this way.

But if you're currently at a point where you're considering discontinuing your AI due to pain or bone loss, ask your doctor about tamoxifen. It looks like the gold standard of hormonal therapy might not be as tarnished as we thought a year or so ago.