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Anastrozole's Ascent

Our featured Pharmaceutical API and relative newcomer to the clinical care scene, anastrozole (also known by the brand name Arimidex) shot to the forefront of post-menopausal breast cancer treatment in the 2000s, after the results of a pivotal trial comparing it to treatment stalwart of two decades tamoxifen.

Tamoxifen, which has been in use since the 1980s, is a selective oestrogen-receptor modulator that inhibits the binding of oestrogen to receptors in the breast; in the three quarters of breast cancers that are oestrogen-receptor positive(ER+) this type of hormone therapy targets the supply of oestrogen that stimulates the cancer’s growth, reducing recurrence rates and improving survival.

While anastrozole works toward the same goal of cutting off the cancer cells’ oestrogen pipeline, it takes a different route. In post-menopausal women the ovaries reduce production of oestrogen, leaving as its main source the conversion of androgenic steroids produced in the adrenal glands. The enzyme aromatase in the fatty tissues, muscle and skin is the catalyst for this conversion – that is, unless an aromatase inhibitor such as anastrozole binds to it first and blocks the androgen conversion in a process called competitive inhibition.

The ATAC (Anastrozole or Tamoxifen, Alone or in Combination) trial results, published in the Lancet in 2002 and 2005, showed that in post-menopausal patients with ER+ breast cancers anastrozole significantly prolonged disease-free survival (recurrence after 10 years was seen in 19.7% anastrozole group and in 24% tamoxifen group) and time to recurrence and reduced distant metastases.

Moreover, common tamoxifen side effects – such as DVT, blood clots and an increased risk of uterine cancer – were not apparent in the anastrozole group. However, its body-wide elimination of oestrogen caused its own issues, primarily a weakening of bones and subsequent increase in fractures. This could be mitigated by taking bone supplements, though, and within a year of finishing the treatment bone density was back to normal1.

The strength of the case for anastrozole led to its widespread adoption as a breast cancer treatment soon after the ATAC study. Subsequent research has shown it to be potentially effective as a breast cancer preventative in high-risk groups as well2, and the National Institute for Health and Care Excellence (NICE) in 2016 recommended it over tamoxifen as a first line preventative treatment3, though it is not yet licensed for this purpose.

Later follow-up to the ATAC trial results reinforced a statistically significant improvement in survival rates over 10 years, though also pointed at a higher incidence of colorectal and lung cancers alongside continued lower rates of endometrial and ovarian cancers and melanoma. Despite these mitigating observations, the authors decided in the final analysis that the data confirmed ‘the long-term superior efficacy and safety of anastrozole over tamoxifen as initial adjuvant therapy’4 and it is widely considered the gold standard of post-menopausal ER+ breast cancer today5.

Where anastrozole is the gold standard in treatment, LGC’s reference APIs are the gold standard of quality control. We are proud to help ensure the safety and consistency of the drugs that save lives around the world every day, and invite you to explore our range of anastrozole products or get in touch to discuss these or any of our other offerings.



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