Breast Cancer: Tamoxifen Metabolite Promising
In the first human experience with a drug that is the main metabolite of tamoxifen, promising responses were observed in woman diagnosed with aromatase inhibitor resistant, metastatic breast cancer, researchers said here.
In a dose-ranging Phase 1 trial that included 22 women, two partial responses were observed and nine women achieved disease stabilization on seven different doses of endoxifen, said Matthew Goetz, MD, deputy director of the Mayo Clinic Breast Cancer Specialized Program of Research Excellence (SPORE), Rochester, Minn.
Ten women progressed while on endoxifen; one woman was not evaluable, Goetz said in his poster discussion sessions at the annual San Antonio Breast Cancer Symposium.
He said that low concentrations of endoxifen were associated with poorer outcomes in both breast cancer patients and in animal models.
He noted that in an animal model of a letrozole resistant xenograft, endoxifen appeared superior to tamoxifen, exemestane and exemestane plus everolimus (RAD001). “The reasons for the superior antitumor activity of endoxifen appears to be complex, and related to the fact that endoxifen is a more potent anti-estrogen, does not activate critical oncogenes involved in nongenomic signaling and may inhibit other kinases.”
The women in the trial were treated at doses from 20 mg to 160 mg. One dose limiting toxicity – a pulmonary embolus – was observed in one patient at the 60 mg dose. The most common grade 2 side effect seen was hot flashes. There was no evidence of eye toxicity on serial dilated eye exams.
When it comes to breast cancer, it’s important to understand that getting regular mammogram screenings is NOT going to prevent anything. In fact, mammography, which employs radiation, can increase your risk since ionizing radiation itself causes cancer… As Dr. Horner writes in her book:
“A European study published in 2012 found that when those who have the genetic predisposition for breast cancer (BRCA1 or BRCA2 gene mutation) are exposed to any diagnostic radiation before age thirty, their risk of breast cancer increases by 90 percent.
The study also found that a history of mammography before age thirty raised the risk by 43 percent. In fact, even one mammogram before the age of thirty for those with the BRCA1 gene mutation was associated with an increased risk.
A newer type of mammogram touted to be much better at detecting breast cancers, called tomosynthesis, takes a 3-D image of the breast. You definitely want to avoid this type of mammogram because it uses three times more radiation than the standard type!”
Furthermore, mammograms:
Are incorrect 80 percent of the time (providing a false negative or false positive)
Use compression, which can damage breast tissue or potentially spread cancer
Are not effective for up to 50 percent of women (women with dense breasts or implants)
Can lead to over-diagnosis and over-treatment of non-invasive cancers
Can lead to the disturbing practice of “preventative” double mastectomies
MRIs, which do not use ionizing radiation, are not a practical tool as they are very expensive, and, like mammograms, they’re not very specific. Ultrasound is another technique used in Western medicine. The traditional ultrasound can see whether a mass is cystic or solid.
But while a solid mass is generally considered to be something that might be of concern, this is not 100 percent certain either, as cancer tumors can sometimes have cysts in them.
In her book, Dr. Horner also mentions another type of ultrasound called “elastography,” which shows the elasticity of tissues.
Cancerous tissue is typically stiffer than healthy tissue, so this ultrasound can identify cancer based on the firmness of the tissues. Several studies published since 2007 have concluded that elastography ultrasound is a useful tool for detecting cancers without using harmful radiation. It also helps reduce the number of unnecessary biopsies from false-positive mammography readings.
Although the maximum tolerated dose of endoxifen was not established in the Phase 1 trial because Goetz and colleagues plan to take the 40 mg a day dose and the 160 mg a day dose further in clinical studies.
Two patients were treated at the 20 mg level; two women received 40 mg; six women received 60 mg, and three women were dosed at 80 mg, 100 mg, 120 mg and 160 mg.
Steven Vogl, MD, a private practice oncologist in The Bronx, told MedPage Today, “There is a subset of women with breast cancer who die because we don’t have any more hormone therapy to give them. We need more of these drugs. Endoxifen is an interesting drug. It looks promising.
“There are all sorts of problems with tamoxifen. Some people can’t convert tamoxifen to the active agent endoxifen; some people take antidepressants that interfere with tamoxifen. Maybe if you gave the real drug, you wouldn’t have to worry about that.”
Breast cancer statistics
In 2009, breast cancer was the most common cancer in Australian women (excluding non-melanoma skin cancer), accounting for 27.4 per cent of all new cancers in women.
In 2009, there were 13,668 new cases of breast cancer in women and 110 new cases in men.
In 2009, the average age of breast cancer diagnosis was 60.7 years.
The risk of developing breast cancer increases with age:
in 2009, 22.9 per cent of new breast cancer cases diagnosed were in women younger than 50 years; 51.4 per cent in women aged 50–69 years; and 25.8 per cent in women aged 70 years and over.
In 2009, the risk of developing breast cancer before the age of 85 in women was 1 in 8.
The incidence of breast cancer in Australia is increasing:
in 2009, the number of new cases of breast cancer diagnosed in women increased to 13,668, from 5,317 in 1982.
in 2020, it is estimated that there will be 17,210 new cases of breast cancer diagnosed in women.
Between 1982 and 1995, the age-standardised incidence rate of breast cancer in women increased from 81.1 to 115.9 per 100,000 women. After this time the rate has remained fairly stable, with the rate in 2009 equalling 113.5 per 100,000 women.
In 2009, the number of men diagnosed with breast cancer in Australia increased to 110, from 61 in 1982.
The median age of the women in the study was 58 years and all were in performance status 0-1. Nine of the women in the study had been on at least three previous treatment regimens and seven women had been on two previous regimens. The remaining women had been on a single previous regimen. In all cases disease had progressed despite treatment.
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Primary source: San Antonio Breast Cancer Symposium
Source reference: Goetz M, et al “Title: A first-in-human phase I study of the tamoxifen metabolite, Z-endoxifen hydrochloride in women with aromatase inhibitor refractory metastatic breast cancer (NCT01327781)” SABCS 2013; Abstract PD3-4.