DCIS (ductal carcinoma in situ) is the most common form of non-invasive breast cancer and is considered stage 0 cancer. While DCIS isn’t life threatening, it increases the risk of developing invasive breast cancer later in life.
DCIS usually is treated with surgery to remove the cancer -- lumpectomy in many cases. After surgery, many women have radiation therapy to reduce the risk of DCIS coming back (recurrence). If the DCIS is hormone-receptor-positive (most are), hormonal therapy also usually is recommended after surgery.
Of the adjuvant hormonal therapy choices, tamoxifen has been approved the longest and is approved to treat both premenopausal and postmenopausal women. Tamoxifen comes in both pill and liquid form and is usually taken once per day.
The other main type of hormonal therapy medicine are the aromatase inhibitors, which are approved to treat only postmenopausal women. The aromatase inhibitors are:
- Arimidex (chemical name: anastrozole)
- Aromasin (chemical name: exemestane)
- Femara (chemical name: letrozole)
Each is a pill, usually taken once a day. All three are available as generic medicines.
A study has found that Arimidex was better than tamoxifen at reducing recurrence risk in postmenopausal women diagnosed with hormone-receptor-positive DCIS.
The study was presented on June 1, 2015 at the American Society of Clinical Oncology Annual Meeting. Read the abstract of “Primary results, NRG Oncology/NSABP B-35: A clinical trial of anastrozole (A) versus tamoxifen (tam) in postmenopausal patients with DCIS undergoing lumpectomy plus radiation.”
In the study, the researchers randomly assigned more than 3,000 postmenopausal women who had been diagnosed with hormone-receptor-positive DCIS to one of two hormonal therapy medicines after lumpectomy and radiation:
- 20 mg per day of tamoxifen
- 1 mg per day of Arimidex
The women took the hormonal therapy medicine they were assigned for 5 years.
After an average follow-up time of about 8 years, the researchers found that:
- 114 breast cancers were diagnosed in the women who took tamoxifen
- 84 breast cancers were diagnosed in the women who took Arimidex
These 198 cancers included recurrences of DCIS as well as new cancers that developed in the same or other breast.
In other words:
- 93.5% of the women who took Arimidex had no recurrence after 10 years
- 89.2% of the women who took tamoxifen had no recurrence after 10 years
This difference was statistically significant, which means that it was likely due to the difference in treatment and not just because of chance.
The researchers also looked to see if Arimidex and tamoxifen offered different benefits to younger or older postmenopausal women:
- For women younger than 60:
- 94.9% of women who took Arimidex had no recurrence after 10 years
- 88.2% of women who took tamoxifen had no recurrence after 10 years
- this difference also was statistically significant
- For women older than 60:
- 92.2% of women who took Arimidex had no recurrence after 10 years
- 90.2% of women who took tamoxifen had no recurrence after 10 years
- this difference was not statistically significant, which means that it could have been due to chance
So for women older than 60, Arimidex and tamoxifen were both equally effective at reducing DCIS recurrence risk.
The researchers said they didn’t have a good explanation for why Arimidex and tamoxifen offered equal benefits to women older than 60.
Both tamoxifen and aromatase inhibitors can cause side effects. Tamoxifen may cause hot flashes and increase the risk of blood clots and stroke. A less common but more severe side effect of tamoxifen is an increase in the risk of uterine cancer. Aromatase inhibitors may cause muscle and joint aches and pains, as well as hot flashes. Less common but more severe side effects of aromatase inhibitors are heart problems, osteoporosis, and broken bones.
When the researchers looked at side effects, they found that women who took Arimidex had more broken bones due to osteoporosis compared to women who took tamoxifen. Women who took tamoxifen had higher rates of uterine cancer than women who took Arimidex. It’s important to know that both these serious side effects were uncommon in the study.
“The good news is tamoxifen and anastrozole are both very effective, but it seems that women have better chances of staying well with anastrozole,” said Richard Margolese, M.D., of The Jewish General Hospital at McGill University in Montreal and lead author of the study. “Women should also consider differences in side effects when discussing treatment options with their doctors.”
“There have been multiple comparisons between tamoxifen and aromatase inhibitors across the spectrum of breast cancer -- in advanced, established metastatic disease for palliation; in the adjuvant setting to prevent recurrence; in the prevention setting for people without cancer; and in the DCIS setting,” said Cliff Hudis, M.D., chief of breast cancer medical services at Memorial Sloan Kettering Cancer Center and member of the Breastcancer.org Professional Advisory Board, in an interview. “And in every setting, the aromatase inhibitor always looks a little bit better on efficacy.
"But the question is more complicated because in the treatment of DCIS or in the prevention setting we are not saving lives, we are preventing events -- another cancer, another breast surgery, and so forth," he continued. "Clinicians and patients are going to continue to struggle with whether they want to take systemic therapy for DCIS and ... which toxicity profile they want to tolerate. The aromatase inhibitors are safer medically but they are difficult to take day by day. It's a bit of an irony that is not lost on people that the drug that is safer causes more day-to-day annoyance. We have to consider the tradeoffs when prescribing these medications.
"I think there is good news to all this," Dr. Hudis concluded. "The good news is that people who want to do something have more options now, not fewer options, and that is good for everybody. The results in the DCIS setting are so favorable anyway that people will have to carefully consider if they want any therapy, and then which one."
If you’re a postmenopausal woman who’s been diagnosed with hormone-receptor-positive DCIS, your doctor will recommend a treatment plan after surgery and radiation that is tailored to your specific risk of recurrence of both DCIS and invasive breast cancer. If you’re considering hormonal therapy after surgery, you might want to talk to your doctor about this study and ask about the risks and benefits of Arimidex and tamoxifen. Together, you can decide on a treatment plan that makes the most sense for you and your unique situation.
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