Effect of anastrozole and tamoxifen as adjuvant treatment for early-stage breast cancer: 10-year analysis of the ATAC trial
- Study type
- Clinical trial
- Study name
- ATAC
- Design
- Randomised controlled trial (registered as ISRCTN18233230); long-term analysis after a median follow-up of 120 months. After treatment completion, fracture and serious adverse event data were collected in a masked fashion.
- Sample size
- Randomised population: 3125 patients in the anastrozole group and 3116 in the tamoxifen group; hormone receptor-positive patients: 2618 anastrozole and 2598 tamoxifen; safety population: 3092 anastrozole and 3094 tamoxifen
- Source
- The Lancet Oncology · 2010
In plain words
In this study, two hormone medicines, anastrozole and tamoxifen, each taken for 5 years, were compared in postmenopausal women with early breast cancer, and patients were followed for about 10 years. Anastrozole lowered the risk of the cancer coming back more than tamoxifen did, especially in women whose cancer was hormone receptor positive. While the medicine was being taken, broken bones were more common with anastrozole, but serious treatment-related side effects were less common. No marked difference in overall deaths was seen between the two groups. The choice of medicine should be made with the treating doctor and based on each patient's circumstances.
Key results
Treatment arms and regimens
Anastrozole 1 mg orally daily for 5 years.
Tamoxifen 20 mg orally daily for 5 years.
Source of the regimen details: Abstract of the paper
Doses are given for the information of specialists, as in this study’s protocol, and are not a prescription. Every drug must be prescribed by the treating physician for the individual patient.
Study population
Postmenopausal women with early-stage breast cancer enrolled for adjuvant treatment. Analyses were performed in all randomised patients and in the hormone receptor-positive subgroup. Other inclusion criteria are not given in the abstract.
Endpoints
Primary endpoint: disease-free survival. Secondary endpoints: time to recurrence, time to distant recurrence, new contralateral breast cancer, overall survival, and death with or without recurrence. Safety (fractures and serious adverse events) was also assessed.
Safety and side effects
Fractures were more frequent in the anastrozole group during active treatment (451 versus 351; OR 1.33; 95% CI 1.15 to 1.55; P<0.0001) but were similar during post-treatment follow-up (110 versus 112; OR 0.98; 0.74 to 1.30; P=0.9).
Treatment-related serious adverse events were less frequent in the anastrozole group (223 versus 369; OR 0.57; 0.48 to 0.69; P<0.0001) but were similar after treatment completion (66 versus 78; OR 0.84; 0.60 to 1.19; P=0.3).
No differences were seen in causes of death not related to breast cancer, and the incidence of other cancers was similar between the two groups (425 versus 431). Colorectal (66 versus 44) and lung (51 versus 34) cancers remained more frequent with anastrozole, and endometrial (6 versus 24), melanoma (8 versus 19) and ovarian (17 versus 28) cancers less frequent. No new safety concerns were reported.
Clinical significance and place in guidelines
This 10-year analysis shows that anastrozole as initial adjuvant therapy in postmenopausal women with hormone-sensitive early breast cancer has long-term superiority over tamoxifen in reducing recurrence and a favourable safety profile; the higher fracture risk was seen only during active treatment. However, no significant difference in overall survival was observed. The status of these findings in current clinical guidelines and drug approvals should be checked separately, as the abstract does not mention them.
Limitations
According to the abstract, the difference in overall survival was not significant (P=0.4) and evidence for a reduction in deaths after recurrence was weak (P=0.09). The carryover benefit after 8 years was smaller. The observed differences in the incidence of other cancers (colorectal, lung, endometrial, melanoma, ovarian) involve small numbers. Other limitations are not given in the abstract and should be checked in the full text.
This summary was prepared by the editorial team from the published paper; the original paper is the final reference. Read the original abstract on PubMed.