‘Arimidex’, Tamoxifen, Alone or in Combination (ATAC) trial: Completed Treatment Analysis

Introduction

Which problems does ATAC address? Is tamoxifen still the best adjuvant therapy for early breast cancer (EBC)? Is anastrozole superior to tamoxifen in the adjuvant setting? Can we improve upon the tolerability problems associated with adjuvant tamoxifen? How do we reduce recurrences in the first few years of treatment?

If tamoxifen is not the best adjuvant treatment: Should anastrozole be considered the preferred initial endocrine therapy? When should anastrozole be given? Is there robust and mature data to support the use of anastrozole in this setting?

Trial design & patient recruitment

     9366 Postmenopausal women with invasive breast cancer mean age 64 years; 84% hormone receptor positive 61% node negative; 64% with tumour  2 cm in diameter Surgery  radiotherapy  chemotherapy Randomisation 1:1:1 for 5 years Anastrozole n=3125 Tamoxifen n=3116 Combination n=3125  Regular follow-up  Primary trial endpoints: Disease-free survival Safety / tolerability Secondary trial endpoints: Incidence of contralateral breast cancer Time to distant recurrence Overall survival Time to breast cancer death Discontinued following initial analysis as no efficacy or tolerability benefit compared with tamoxifen arm ATAC trial design

ATAC completed treatment analysis Follow-up: –Data cut-off 31st March 2004, based on at least 704 deaths in the two monotherapy arms combined –68 months’ median follow-up – beyond completion of treatment –59 months’ median treatment duration –Only 8% of patients remain on treatment – the great majority of these nearing completion Results: –Anastrozole demonstrates superior efficacy to tamoxifen –Anastrozole demonstrates superior tolerability to tamoxifen –The results of this analysis are mature and the overall risk:benefit profile of anastrozole can be considered final

Efficacy analysis

Smoothed hazard rates for recurrence ( HR*-positive population ) Follow-up time (years) Annual hazard rates (%) Anastrozole Tamoxifen *HR=hormone receptor

A T Disease-free survival (HR*-positive population) p-value HR 0.83 A vs T 95% CI (0.73–0.94) At risk: Follow-up time (years) Anastrozole (A) Tamoxifen (T) Patients (%) Absolute difference: 1.6%2.6%2.5%3.3% *HR=hormone receptor

A T Recurrence (HR*-positive population) Anastrozole (A) Tamoxifen (T) p-value HR 0.74 A vs T 95% CI (0.64–0.87) Follow-up time (years) At risk: Patients (%) Absolute difference: 1.7%2.4%2.8%3.7% *HR=hormone receptor

Analysis of time to recurrence for subgroups of the HR*-positive population Nodal status+ve -ve unknown** Tumour size  2 cm 2–5 cm >5 cm* Previous chemotherapy Yes No All patients *HR=hormone receptor Anastrozole betterTamoxifen better **Confidence limit extends beyond plot Hazard ratio (A:T) and 95% CI

A T Time to distant recurrence (HR*-positive population) p-value 0.06 HR 0.84 A vs T 95% CI (0.70–1.00) Anastrozole (A) Tamoxifen (T) Follow-up time (years) At risk: Patients (%) *HR=hormone receptor

A T Overall survival (HR*-positive population) p-value 0.7 HR 0.97 A vs T 95% CI (0.83–1.14) Anastrozole (A) Tamoxifen (T) Follow-up time (years) At risk: Patients (%) *HR=hormone receptor

Incidence of new (contralateral) breast primaries in HR*- population *p=0.001 for invasive cancers. *HR=hormone receptor 21 Invasive* 53 Tamoxifen (TAM) (n=3116) Anastrozole (AN) (n=3125) 26 5 DCIS HR95% CIp-value AN vs TAM – Invasive* Number of cases 5 DCIS

Recurrence rate/year (%) Year Saphner et al JCO 1996; 14: Most recurrences occur within the first 5 years of primary therapy Need to give most effective treatment first to reduce risk of recurrence

A T Disease-free survival (HR*-positive population) p-value HR 0.83 A vs T 95% CI (0.73–0.94) At risk: Follow-up time (years) Anastrozole (A) Tamoxifen (T) Patients (%) Absolute difference: 1.6%2.6%2.5%3.3% *HR=hormone receptor

Anastrozole demonstrates superior efficacy to tamoxifen Anastrozole is more effective than tamoxifen in reducing the risk of recurrence, distant recurrence and contralateral breast cancer The absolute difference between anastrozole and tamoxifen continues to increase over time, and extends beyond completion of treatment As expected, overall survival is similar for both treatments, with a trend in favour of anastrozole for breast cancer death There are no significant subgroup interactions

Added benefit versus tamoxifen Hormone receptor-positive population Reduction in risk of recurrence Reduction in risk of breast cancer mortality Reduction in risk of contralateral breast cancer EBCTCG Benefit for tamoxifen vs placebo 50% 28% 47%* ATAC Additional benefit of anastrozole vs tamoxifen 26% 13% 52% *hormone receptor-positive and -negative patients EBCTCG = Early Breast Cancer Trialists’ Collaborative Group

Added benefit versus tamoxifen 38% risk of recurrence with no adjuvant treatment 50% reduction in risk with tamoxifen Further 26% risk reduction with anastrozole

When to treat? Recurrence rates I early breast cancer are highest in the first 5 years after surgery, with a peak at 2 years, regardless of baseline prognostic factors Tamoxifen is associated with higher rates of recurrence, AEs and withdrawals than anastrozole Substantial benefit with anastrozole in the first 3 years justifies offering the most effective therapy at the earliest opportunity

Tolerability analysis

Overview of adverse events* All adverse events Adverse events leading to withdrawal Drug-related adverse events leading to withdrawal All serious adverse events Serious adverse events leading to withdrawal Serious adverse events leading to death Drug-related serious adverse events leading to death p-value Tamoxifen (%) (n=3094) Anastrozole (%) (n=3092) *Adverse events on treatment or within 14 days of discontinuation

T A Completion analysis p-value < < Hot flushes Vaginal bleeding Vaginal discharge Endometrial cancer* Ischaemic cerebrovascular event Venous thromboembolic events Deep venous thromboembolic events Joint symptoms Total fractures *Excludes patients with prior hysterectomy and includes on- and off-therapy AEs Pre-defined adverse events

Fractures Hot flushes Joint symptoms Venous thromboembolic events Ischaemic cerebrovascular events Endometrial cancer Vaginal bleeding Vaginal discharge Relative risk (anastrozole / tamoxifen) In favour of anastrozoleIn favour of tamoxifen

Tolerability summary Compared with tamoxifen, anastrozole is associated with significantly fewer: –SAEs, treatment-related AEs and withdrawals due to SAEs or AEs –potentially life threatening AEs such as endometrial cancer, thromboembolic, and cerebrovasular events No new safety concerns have emerged with long-term follow-up Only anastrozole has a tolerability profile of this robustness and maturity, as it covers the full 5 year treatment period Anastrozole now has a known, predictable and manageable safety profile

Summary

ATAC summary ATAC Completed Treatment Analysis extends and strengthens the evidence that 5 years of anastrozole is significantly more effective and better tolerated than 5 years of tamoxifen Overall risk:benefit profile remains clearly in favour of anastrozole The absolute benefits for anastrozole over and above those of tamoxifen continue to increase with time and extend beyond the completion of therapy

ATAC in context Anastrozole is a more effective and better-tolerated adjuvant treatment than tamoxifen These findings provide a basis for establishing anastrozole as the standard of care for the initial 5 years’ adjuvant treatment of postmenopausal women with hormone receptor-sensitive early breast cancer Howell, SABCS 2004

Back-up slides

Definition of endpoints (1) Disease-free survival (DFS) –loco-regional recurrence (inc. ipsilateral new breast cancer) or new contralateral breast cancer –distant recurrence or death (for any reason) Distant disease-free survival (DDFS) –distant recurrence –death (for any reason) Time to recurrence (TTR) –loco-regional recurrence (inc. ipsilateral new breast cancer) or new contralateral breast cancer –distant recurrence or death due to breast cancer

Definition of endpoints (2) Overall survival (OS) –death (for any reason) Time to distant recurrence (TTDR) –distant recurrence or any death following a loco- regional recurrence (inc. ipsilateral new breast cancer) –breast cancer death Time to breast cancer death (TTBCD) –any death following a loco-regional (inc. ipsilateral new breast cancer) or distant recurrence –breast cancer death

ATAC: patient characteristics Tamoxifen (n=3116) Anastrozole (n=3125) Mean age (years) Mean weight (kg) Receptor status (%) positive negative unknown Primary treatment (%) mastectomy axillary surgery radiotherapy chemotherapy prior tamoxifen

ATAC: baseline disease characteristics Primary tumour size (%) T1 (  2 cm) T2 (  2 cm to  5 cm) T3 (  5 cm) Nodal status (%) node-positive Grading (%) well differentiated moderately differentiated poorly / undifferentiated not assessed / recorded Tamoxifen (n=3116) Anastrozole (n=3125)

ATAC trial analysis history First analysis – June 2002 Median follow-up : 33 months 1 Updated analysis – November 2003 Median follow-up : 47 months 2 Completion analysis – November 2004 Median follow-up : 68 months Women years’ follow up: 49,941 Total events: The ATAC Trialists’ Group. Lancet 2002; 359: 2131– The ATAC Trialists’ Group. Cancer 2003; 98: 1802 – 1810

Smoothed hazard rates for recurrence (ITT* population) Follow-up time (years) Annual hazard rates (%) Anastrozole Tamoxifen 0 *ITT=intent-to-treat

At risk: A T Follow-up time (years) Includes non breast cancer deaths *ITT=intent-to-treat Disease-free survival (ITT* population) p-value HR 0.87 A vs T 95% CI (0.78–0.97) Anastrozole (A) Tamoxifen (T) Patients (%) Absolute difference: 1.5%2.0%2.4%2.9%

A T p-value HR 0.79 A vs T 95% CI (0.70–0.90) Follow-up time (years) At risk: Recurrence (ITT* population) Anastrozole (A) Tamoxifen (T) Patients (%) Absolute difference: 1.6%2.1%2.8%3.4% *ITT=intent-to-treat

**Confidence limit extends beyond plot Analysis of time to recurrence for subgroups of the ITT* population Hazard ratio (A:T) and 95% CI Nodal status+ve -ve unknown All patients Tumour size≤ 2 cm >2 cm unknown** Receptor status+ve -ve unknown Previous chemotherapy yes no Anastrozole betterTamoxifen better *ITT=intent-to-treat

A T At risk: p-value HR 0.86 A vs T 95% CI (0.74–0.99) Follow-up time (years) Time to distant recurrence (ITT* population) Anastrozole (A) Tamoxifen (T) Patients (%) *ITT=intent-to-treat

A T p-value 0.7 HR 0.97 A vs T 95% CI (0.85–1.12) At risk: Follow-up time (years) Overall survival (ITT* population) Anastrozole (A) Tamoxifen (T) Patients (%) Includes non breast cancer deaths *ITT=intent-to-treat

A T p-value 0.2 HR 0.88 A vs T 95% CI (0.74–1.05) At risk: Follow-up time (years) Time to breast cancer death (ITT* population) Anastrozole (A) Tamoxifen (T) Patients (%) *ITT=intent-to-treat

Incidence of new (contralateral) breast primaries in ITT* population 27 Invasive* 58 Tamoxifen (TAM) (n=3116) Anastrozole (AN) (n=3125) 35 6 DCIS HR95% CIp-value AN vs TAM – Invasive* Number of cases 8 DCIS *p=0.004 for invasive cancers. *ITT=intent-to-treat

Summary of efficacy endpoints In the overall ITT population, compared with tamoxifen, anastrozole provides significantly reduced risk of : –all events: 13% (p=0.013) –recurrence: 21% (p=0.0005) –distant recurrence: 14% (p=0.043) –contralateral recurrence: 42% (p=0.01)