ARIMIDEX^® (anastrozole)

Indication

ARIMIDEX is indicated for adjuvant treatment of postmenopausal women with hormone receptor-positive early breast cancer.

ARIMIDEX is indicated for the first-line treatment of postmenopausal women with hormone receptor-positive or hormone receptor-unknown locally advanced or metastatic breast cancer. ARIMIDEX is indicated for the treatment of advanced breast cancer in postmenopausal women with disease progression following tamoxifen therapy. Patients with estrogen receptor-negative disease and patients who did not respond to previous tamoxifen therapy rarely responded to ARIMIDEX.

See how ARIMIDEX works.

Mechanism of Action

The growth of many cancers of the breast is stimulated or maintained by estrogens. Treatment of breast cancer thought to be hormonally responsive (ie, estrogen and/or progesterone receptor-positive or receptor-unknown) has included a variety of efforts to decrease estrogen levels (ovariectomy, adrenalectomy, hypophysectomy) or inhibit estrogen effects (antiestrogens and progestational agents). These agents lead to decreased tumor mass or delayed progression of tumor growth in some women.

In postmenopausal women, estrogens are mainly derived from the action of the aromatase enzyme, which converts adrenal androgens (primarily androstenedione and testosterone) to estrone and estradiol. The suppression of estrogen biosynthesis in peripheral tissues and in the cancer tissue itself can therefore be achieved by specifically inhibiting the aromatase enzyme.

Anastrozole is a potent and selective non-steroidal aromatase inhibitor. It significantly lowers serum estradiol concentrations and has no detectable effect on formation of adrenal corticosteroids or aldosterone.

Safety

ARIMIDEX is only for postmenopausal women. ARIMIDEX can cause fetal harm when administered to a pregnant woman. Before starting treatment with ARIMIDEX, pregnancy must be excluded (see CONTRAINDICATIONS section of full Prescribing Information).

In women with preexisting ischemic heart disease 465/6186 (7.5%), an increased incidence of ischemic cardiovascular events occurred with ARIMIDEX (17%) vs tamoxifen (10%). In this patient population, angina pectoris was reported in 25/216 (11.6%) vs 13/249 (5.2%) and myocardial infarction was reported in 2/216 (0.9%) vs 8/249 (3.2%) patients receiving ARIMIDEX and tamoxifen, respectively.

Compared to baseline, ARIMIDEX showed a mean decrease in both lumbar spine and total hip bone mineral density. Tamoxifen showed a mean increase in these measurements. Nine percent of patients receiving ARIMIDEX had an elevated serum cholesterol vs 3.5% of patients receiving tamoxifen.

Common side effects seen with ARIMIDEX vs tamoxifen in the early breast cancer trial after 5 years of treatment include hot flashes (36% vs 41%), joint disorders (including arthritis, arthrosis, arthralgia) (36% vs 29%), asthenia (19% vs 18%), mood disturbances (19% vs 18%), pain (17% vs 16%), pharyngitis (14% vs 14%), nausea and vomiting (13% vs 12%), rash (11% vs 13%), depression (13% vs 12%), hypertension (13% vs 11%), osteoporosis (11% vs 7%), peripheral edema (10% vs 11%), lymphedema (10% vs 11%), back pain (10% vs 10%), insomnia (10% vs 9%), and headache (10% vs 8%). Fractures, including fractures of the spine, hip, and wrist, occurred more often with ARIMIDEX vs tamoxifen (10% vs 7%).

In the advanced breast cancer studies, the most common (occurring with an incidence of >10%) side effects occurring in women taking ARIMIDEX included hot flashes, nausea, asthenia, pain, headache, back pain, bone pain, increased cough, dyspnea, pharyngitis, and peripheral edema. Joint pain/stiffness has been reported in association with the use of ARIMIDEX.

Clinical and pharmacokinetic results suggest that tamoxifen should not be administered with ARIMIDEX. Estrogen-containing therapies should not be used with ARIMIDEX as they may diminish its pharmacologic action.

Dosing

The dose of ARIMIDEX is one 1 mg tablet taken once a day. For patients with advanced breast cancer, ARIMIDEX should be continued until tumor progression. ARIMIDEX can be taken with or without food.

For adjuvant treatment of early breast cancer in postmenopausal women, the optimal duration of therapy is unknown. In the ATAC trial, ARIMIDEX was administered for 5 years.

Efficacy

Adjuvant Treatment of Breast Cancer in Postmenopausal Women
A multicenter, double-blind trial (ATAC) randomized 9,366 postmenopausal women with operable breast cancer to adjuvant treatment with ARIMIDEX 1 mg daily, tamoxifen 20 mg daily, or a combination of the two treatments for five years or until recurrence of the disease.

The primary endpoint of the trial was disease-free survival (i.e., time to occurrence of a distant or local recurrence, or contralateral breast cancer or death from any cause). Secondary endpoints of the trial included distant disease-free survival, the incidence of contralateral breast cancer and overall survival. At a median follow-up of 33 months, the combination of ARIMIDEX and tamoxifen did not demonstrate any efficacy benefit when compared with tamoxifen in all patients as well as in the hormone receptor-positive subpopulation. This treatment arm was discontinued from the trial. Based on clinical and pharmacokinetic results from the ATAC trial, tamoxifen should not be administered with anastrozole [see Drug Interactions (7.1)].

Demographic and other baseline characteristics were similar among the three treatment groups (see Table 1).

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Patients in the two monotherapy arms of the ATAC trial were treated for a median of 60 months (5 years) and followed for a median of 68 months. Disease-free survival in the intent-to-treat population was statistically significantly improved [Hazard Ratio (HR) = 0.87, 95% CI: 0.78, 0.97, p=0.0127 in the ARIMIDEX arm compared to the tamoxifen arm. In the hormone receptor-positive subpopulation representing about 84% of the trial patients, disease-free survival was also statistically significantly improved (HR =0.83, 95% CI: 0.73, 0.94, p=0.0049) in the ARIMIDEX arm compared to the tamoxifen arm.

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The survival data with 68 months follow-up is presented in Table 2.

In the group of patients who had previous adjuvant chemotherapy (N=698 for ARIMIDEX and N=647 for tamoxifen), the hazard ratio for disease-free survival was 0.91 (95% CI: 0.73 to 1.13) in the ARIMIDEX arm compared to the tamoxifen arm.

The frequency of individual events in the intent-to-treat population and the hormone receptor-positive subpopulation are described in Table 2.

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A summary of the study efficacy results is provided in Table 3.

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First-Line Therapy in Postmenopausal Women with Advanced Breast Cancer
Two double-blind, controlled clinical studies of similar design (0030, a North American study and 0027, a predominately European study) were conducted to assess the efficacy of ARIMIDEX compared with tamoxifen as first-line therapy for hormone receptor-positive or hormone receptor-unknown locally advanced or metastatic breast cancer in postmenopausal women. A total of 1021 patients between the ages of 30 and 92 years old were randomized to receive trial treatment. Patients were randomized to receive 1 mg of ARIMIDEX once daily or 20 mg of tamoxifen once daily. The primary end points for both trials were time to tumor progression, objective tumor response rate, and safety.

Demographics and other baseline characteristics, including patients who had measurable and no measurable disease, patients who were given previous adjuvant therapy, the site of metastatic disease and ethnic origin were similar for the two treatment groups for both trials. The following table summarizes the hormone receptor status at entry for all randomized patients in trials 0030 and 0027.

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For the primary endpoints, trial 0030 showed that ARIMIDEX had a statistically significant advantage over tamoxifen (p=0.006) for time to tumor progression; objective tumor response rates were similar for ARIMIDEX and tamoxifen. Trial 0027 showed that ARIMIDEX and tamoxifen had similar objective tumor response rates and time to tumor progression (see Table 5 and Figure 3 and 4).

Table 5 below summarizes the results of trial 0030 and trial 0027 for the primary efficacy endpoints.

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Results from the secondary endpoints were supportive of the results of the primary efficacy endpoints. There were too few deaths occurring across treatment groups of both trials to draw conclusions on overall survival differences.

Second-Line Therapy in Postmenopausal Women with Advanced Breast Cancer who had Disease Progression following Tamoxifen Therapy
Anastrozole was studied in two controlled clinical trials (0004, a North American study; 0005, a predominately European study) in postmenopausal women with advanced breast cancer who had disease progression following tamoxifen therapy for either advanced or early breast cancer. Some of the patients had also received previous cytotoxic treatment. Most patients were ER-positive; a smaller fraction were ER-unknown or ER-negative; the ER-negative patients were eligible only if they had had a positive response to tamoxifen. Eligible patients with measurable and non-measurable disease were randomized to receive either a single daily dose of 1 mg or 10 mg of ARIMIDEX or megestrol acetate 40 mg four times a day. The studies were doubleblinded with respect to ARIMIDEX. Time to progression and objective response (only patients with measurable disease could be considered partial responders) rates were the primary efficacy variables. Objective response rates were calculated based on the Union Internationale Contre le Cancer (UICC) criteria. The rate of prolonged (more than 24 weeks) stable disease, the rate of progression, and survival were also calculated.

Both trials included over 375 patients; demographics and other baseline characteristics were similar for the three treatment groups in each trial. Patients in the 0005 trial had responded better to prior tamoxifen treatment. Of the patients entered who had prior tamoxifen therapy for advanced disease (58% in Trial 0004; 57% in Trial 0005), 18% of these patients in Trial 0004 and 42% in Trial 0005 were reported by the primary investigator to have responded. In Trial 0004, 81% of patients were ER-positive, 13% were ER-unknown, and 6% were ER-negative. In Trial 0005, 58% of patients were ER-positive, 37% were ER-unknown, and 5% were ER-negative. In Trial 0004, 62% of patients had measurable disease compared to 79% in Trial 0005. The sites of metastatic disease were similar among treatment groups for each trial. On average, 40% of the patients had soft tissue metastases; 60% had bone metastases; and 40% had visceral (15% liver) metastases.

Efficacy results from the two studies were similar as presented in Table 6. In both studies there were no significant differences between treatment arms with respect to any of the efficacy parameters listed in table 6 below.

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When data from the two controlled trials are pooled, the objective response rates and median times to progression and death were similar for patients randomized to ARIMIDEX 1 mg and megestrol acetate. There is, in this data, no indication that ARIMIDEX 10 mg is superior to ARIMIDEX 1 mg.

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