In view of the new data from the ATAC trial, should anastrozole now be used as adjuvant therapy for postmenopausal women with early invasive breast cancer?

OVERVIEW: Tamoxifen has been the predominant form of adjuvant endocrine therapy since the first International Breast Cancer Overview was presented at the 1985 NIH Consensus Conference. Currently, most patients with invasive estrogen receptor-positive cancers are treated with tamoxifen regardless of age, menopausal status and risk to recur. On December 10, 2001, the initial results of the ATAC trial were presented at the San Antonio Breast Cancer Symposium. These groundbreaking data demonstrated that in postmenopausal women with primary invasive breast cancer, the third generation aromatase inhibitor, anastrozole, conferred an advantage over tamoxifen in terms of efficacy, tolerability and toxicity. No advantage was observed to combining anastrozole with tamoxifen. Clinicians and patients are now struggling with the clinical implications of these early but very promising results from the largest cancer treatment trial ever conducted.

ONCOLOGISTS

Which of the following describes how you generally identify a breast cancer as being ER-positive?

DISEASE		ANY STAINING	STAINING ABOVE A SPECIFIC CUT-OFF AS DEFINED BY THE LAB DOING THE TEST
ER-positive breast cancer		50%	50%

Which adjuvant endocrine therapy would you recommend for the following patients with ER-positive, HER2-negative breast cancer?

		TAMOXIFEN	ANASTROZOLE	LETROZOLE	NONE/OTHER
	65-year-old woman with a 2.2 cm tumor/10+ nodes	60%	30%	5%	5%
	65-year-old woman with a 2.2 cm tumor/2+ nodes	50%	40%	5%	5%
	65-year-old woman with a 2.2 cm tumor/neg nodes	55%	35%	5%	5%
	65-year-old woman with a 0.8 cm tumor/neg nodes	35%	35%	10%	20%
	77-year-old woman with a 2.2 cm tumor/10+ nodes	50%	40%	10%	0%
	77-year-old woman with a 0.8 cm tumor/neg nodes	35%	15%	5%	45%

SURGEONS

How would you manage the following patients with ER+, HER2-negative breast cancer?

		REFER TO ONCOLOGIST	START TAMOXIFEN	START ANASTROZOLE	MANAGE WITHOUT ADJUVANT SYSTEMIC THERAPY	MANAGE PT. PRIMARILY WITH TAMOXIFEN
	65-year-old woman with a 0.8 cm tumor/neg nodes	50%	5%	40%	5%	5%
	65-year-old woman with a 2.2 cm tumor/neg nodes	75%	10%	10%	5%	-
	65-year-old woman with a 1.2 cm tumor/1+ node	85%	5%	10%	-	-
	77-year-old woman with a 0.8 cm tumor/neg nodes	50%	-	30%	5%	15%

 

ONCOLOGISTS

Which of the following best describes your intended use in the near future of aromatase inhibitors as adjuvant therapy?

SURGEONS

If the ATAC data are widely accepted, and anastrozole generally replaces tamoxifen as adjuvant endocrine therapy for postmenopausal women, how likely is it that surgeons will prescribe anastrozole?

Surgeons will prescribe anastrozole	VERY LIKELY	LIKELY	SOMEWHAT LIKELY	VERY UNLIKELY	UNDETERMINED
	30%	25%	25%	15%	5%

 

SUMMARY OF ATAC RESULTS

The headline news is that there is something after tamoxifen — there is a significant advantage for anastrozole compared to tamoxifen. The real surprise is that the combination of anastrozole and tamoxifen is no different than tamoxifen alone. What makes these early ATAC results even more extraordinary is that about 15% of the trial population was ER-negative and ER unknown. When you look at the analysis of the known ER-positive patients, the results are even stronger. The hazard ratio for anastrozole compared to tamoxifen is 0.78. This is equivalent to a 22% relative reduction in risk of recurrence compared to tamoxifen.

—Michael Baum, ChM, FRCS

OUTCOMES OF THE ATAC TRIAL

I think it’s very surprising that the benefit of anastrozole emerged so clearly and so strongly. We’re talking about almost a 25% reduction in recurrence compared to tamoxifen in estrogen receptor-positive women. Tamoxifen itself produces about a 40% reduction in recurrence rates, so to get another 25% on top of that is really quite substantial. Even more, we are seeing these results with a side effect profile that is generally more favorable.

However, these are the early days for a new drug that produces very, very low estrogen levels. Clearly, these low levels affect the bones and there is concern that they might affect memory and cognitive function as well. These are probably manageable problems, but this is one of the areas where we need to be cautious.

—Jack Cuzick, PhD

SIDE EFFECTS AND TOXICITIES WITH TAMOXIFEN AND ANASTROZOLE

ATAC demonstrated that fewer side effects are associated with anastrozole than tamoxifen. Thromboembolic complications, vaginal bleeding, spotting and discharge, and endometrial cancer were all substantially lower in the anastrozole arm.

In terms of the side effects seen with anastrozole, I have not seen any patient in which arthralgias forced us to change or stop therapy. The potential negative effects on bone of anastrozole can be watched very closely. If there is a change in bone density, highly-effective interventions can be pr ovided.

—Aman Buzdar, MD

SUBSTITUTING OTHER AROMATASE INHIBITORS IN THE ADJUVANT SETTING

There are no data to support using letrozole or exemestane in the adjuvant setting. Since anastrozole is the only drug that’s been tested, it is the drug we should use. All of the aromatase inhibitors are slightly different. We need direct comparative data for these drugs. If they are equally effective, it might come down to which one has the fewest side effects and best tolerability. Until we have comparative data, the drug which has been tested in the adjuvant setting should be used.

—J Michael Dixon, MD, FRCS

ADJUVANT ENDOCRINE TREATMENT: IMPLICATIONS OF ATAC

In the evolution of science and medicine there are periods of uncertainty. We are living in such a time now. If the efficacy advantage for anastrozole continues, then we can start making therapeutic recommendations. Presently we have only two and one-half years of treatment data. We cannot be certain about what will happen with further therapy.

Newly diagnosed women should be informed of the ATAC data in a responsible way. Most of them will make a rational decision. I believe that tamoxifen should continue to be considered the gold standard, at least until the trial results are updated at ASCO 2002. However, my colleagues have been putting some adjuvant patients on anastrozole on the basis of the positive findings in the metastatic setting — without the adjuvant data — and it is a legitimate non-protocol option where there are contraindications to tamoxifen. If women are already on adjuvant tamoxifen, it would be hazardous to switch to anastrozole, since we haven’t tested that sequential therapeutic rapproach.

—Michael Baum, ChM, FRCS

The only shortcoming of the ATAC data is the relatively short follow-up period. Of course, everyone would like to see drugs followed for 20-30 years, but we can’t decide the fate of the patients while waiting for the data to become that mature. In the ATAC trial, there is a significant reduction in the risk of recurrence and fewer side effects and fewer potentially lethal complications associated with anastrozole compared to tamoxifen. It is my responsibility as a physician to share information with patients and let them be active participants in making their own decisions. However, if I were a patient, I would opt for anastrozole even though there is a short period of follow-up.

—Aman Buzdar, MD

3RD GENERATION AROMATASE INHIBITORS

 

ATAC TRIAL - STUDY ENDPOINTS PRIMARY ENDPOINTS Disease-free survival Locoregional or distant recur rence, new primary breast cancer, or death from any cause Safety/Tolerability SECONDARY ENDPOINTS Incidence of new breast (contral ateral) primaries Time to distant recurrence Survival (data will be mature in » 2 years) Hormone rece ptor-positive population (protocol-defined sub-group)

 

ATAC TRIAL - PATIENT CHARACTERISTICS* Mean age in the anastrozole arm was 64.1 years      • 83.7% of patients in the anastrozole arm were ER-positive      • 47.8% of patients in the anastrozole arm were treated with mastectomy      • 22.3% of patients in the anastrozole arm were treated with chemot herapy *patients in all arms were similar

 

ANASTROZOLE’S PROFILE Highly selective, potent aromatase inhibitor Non-steroidal Orally active (1 mg) Once-daily dosing Superior to tamoxifen in postmenopausal women with estrogen receptor-positive advanced breast cancer Survival advantage vs. megestrol acetate in metastatic disease Over 460,000 patient-years experience

 

ATAC TRIAL DESIGN - POSTMENOPAUSAL WOMEN WITH INVASIVE BREAST CANCER

 

SUBPROTOCOLS OF THE ATAC TRIAL Hormone rece ptor-positive population (protocol-defined sub-group) Pharmacodynamic and pharmacokinetic profiles Modulation of lipoprotein profiles Endometrial status Bone mineral metabolism Quality of life

 

ON-GOING RANDOMIZED TRIALS OF POST-TAMOXIFEN AROMATASE INHIBITORS IN POSTMENOPAUSAL BREAST CANCER PATIENTS

Post-Tamoxifen Treatment Adjuvant Tamoxifen (years) Projected Accrual Sponsor Letrozole 5 years 4.5 - 6 4,800 Canadian NCI, NCCTG, & SWOG CALGB, EORTC Exemestane 2 years 5 3,000 NSABP Exemestane 2 - 3 years 2 - 3 4,400 Breast International Group Anastrozole 3 years 5 1,700 Austrian Breast & Colon Cancer Study Group TRIALS OF AROMATASE INHIBITORS AFTER TAMOXIFEN We've got adjuvant studies that look at aromatase inhibitors given after tamoxifen. The question now is, a re those studies going to be re l e vant anymore? Is it really the studies that use aromatase inhibitors up front that are going to be the ones we're interested in? We may have a whole group of large studies with interesting information that we may not use, because we won’t be giving the drugs that way anymore. —Kathleen Pritchard ,M D

 

SUMMARY OF ATAC TRIAL OUTCOMES 9,366 evaluable patients Atamedian treatment duration of 2.5 years , anastrozole demonstrated superior efficacy and tolerability compared to tamoxifen Anastrozole was superior to tamoxifen in terms of disease-free survival in the overall population (relative reduction of 17%) and in estrogen receptor-positive patients (relative reduction of 22%) Anastrozole was superior to tamoxifen in terms of the incidence of contralateral breast cancer in the overall population (relative reduction of 58%) There were 156 patients with distant metastases in the anastrozole arm and 181 in the tamoxifen arm (not statistically different ) • There were only a total of five breast cancer deaths in the three treatment arms Anastrozole was tolerated better than tamoxifen with respect to: Endometrial cancer Vaginal bleeding Vaginal discharge Is chaemic cerebrovascular events Venous thromboembolic events Hot flashes Weight gain Tamoxifen was tolerated better than anastrozole with respect to: Musculos keletal disorders (arthralgias) Fractures Derived from a presentation by Michael Baum, 24th Annual San Antonio B reast Cancer Symposium Baum M. The ATAC (Arimidex, Tamoxifen, Alone or in Combination) adjuvant breast cancer trial in postmenopausal (PM) women. Breast Cancer Res Treat 2001; 69(3):Abstact.

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