Trial results showed a slight advantage for Arimidex over tamoxifen in treating early breast cancer in post-menopausal women. However, ASCO has advised caution in replacing tamoxifen with AstraZeneca's drug. Although this verdict will hold sales back in the short term, there is still huge long-term potential for Arimidex as the preferred breast cancer therapy.
An American Society of Clinical Oncology (ASCO) panel has said that physicians should not switch from tamoxifen to AstraZeneca's Arimidex as the front-line treatment for early breast cancer in post-menopausal women.
For the last 16 years, tamoxifen has been the standard drug to prevent recurrence of breast cancer after surgery. However, in December 2001, researchers reported 33-month results from the five-year ongoing ATAC study comparing AstraZeneca's aromatase inhibitor Arimidex with tamoxifen. Arimidex appeared slightly more effective and safer than tamoxifen.
In view of December's findings, ASCO appointed a panel to assess Arimidex's effectiveness and safety. But while the panel believes the results are encouraging, it says 33 months is too short a period to judge the safety and effectiveness of aromatase inhibitors as standard therapy: usually, women take tamoxifen for five years. The panel also says there is no evidence so far that Arimidex improves women's survival.
Until 2000, Arimidex's revenue potential was limited by its approval only as a second-line therapy in patients who were refractory to tamoxifen. However, after clinical trials showed Arimidex's clinical advantages in slowing tumor progression, it was also approved in Europe and the US as first-line therapy for advanced breast cancer. This approval brought a significant increase in patient potential, as tamoxifen currently dominates breast cancer therapy.
AstraZeneca already leads the anticancer hormonals market. With the combination of the study results so far and the company's aggressive marketing strategies and expertise, it will have a strong chance of keeping the lead position, despite losing on the generics market after tamoxifen's patent expiry.
The ASCO decision will slow down Arimidex's short-term expansion, leaving physicians cautious of prescribing the drug instead of tamoxifen. However, if the final study results are as promising as the preliminary data, Arimidex will be a very successful product on a huge market, with a major impact on AstraZeneca's revenues.
Related research: Datamonitor, 2002: "Drugs of Tomorrow 2002 Breast Cancer"