Mechanism of Action
The HER2 (or c‑erbB2) proto‑oncogene encodes a transmembrane receptor protein of 185 kDa, which is structurally related to the epidermal growth factor receptor. Herceptin has been shown, in both in vitro assays and in animals, to inhibit the proliferation of human tumor cells that overexpress HER2.
Herceptin is a mediator of antibody‑dependent cellular cytotoxicity (ADCC). In vitro, Herceptin‑mediated ADCC has been shown to be preferentially exerted on HER2 overexpressing cancer cells compared with cancer cells that do not overexpress HER2.
The pharmacokinetics of trastuzumab were studied in women with metastatic breast cancer. Short duration intravenous infusions of 10 to 500 mg Herceptin once weekly demonstrated dose‑dependent pharmacokinetics. Mean half‑life increased and clearance decreased with increasing dose level. The half‑life averaged 2 and 12 days at the 10 and 500 mg dose levels, respectively. The volume of distribution of trastuzumab was approximately that of serum volume (44 mL/kg). At the highest weekly dose studied (500 mg), mean peak serum concentrations were 377 mcg/mL.
In studies using an initial dose of 4 mg/kg followed by a weekly dose of 2 mg/kg, a mean half‑life of 6 days (range 1—32 days) was observed. Between weeks 16 and 32, trastuzumab serum concentrations reached a steady state with mean trough and peak concentrations of approximately 79 mcg/mL and 123 mcg/mL, respectively.
In a study of women receiving adjuvant therapy for breast cancer, a mean half‑life of trastuzumab of 16 days (range: 11—23 days) was observed after an initial dose of 8 mg/kg followed by a dose of 6 mg/kg every three weeks. Between weeks 6 and 37, trastuzumab serum concentrations reached a steady‑state with mean trough and peak concentrations of 63 mcg/mL and 216 mcg/mL, respectively.
Sixty‑four percent (286/447) of women with metastatic breast cancer had detectable circulating extracellular domain of the HER2 receptor (shed antigen), which ranged as high as 1880 ng/mL (median 11 ng/mL). Patients with higher baseline shed antigen levels were more likely to have lower serum trough concentrations.
Data suggest that the disposition of trastuzumab is not altered based on age or serum creatinine (≤ 2.0 mg creatinine/dL).
Mean serum trough concentrations of trastuzumab, when administered in combination with paclitaxel, were consistently elevated approximately 1.5‑fold as compared with serum concentrations of trastuzumab when used in combination with anthracycline plus cyclophosphamide. In clinical studies in HER2+ metastatic breast cancer where Herceptin was administered in combination with paclitaxel, in combination with docetaxel, or in combination with paclitaxel and doxorubicin, Herceptin did not appear to alter the plasma concentrations of these chemotherapeutic agents, or the metabolites that were analyzed.
Carcinogenesis, Mutagenesis, Impairment of Fertility
Herceptin has not been tested for its carcinogenic potential.
No evidence of mutagenic activity was observed when trastuzumab was tested in the standard Ames bacterial and human peripheral blood lymphocyte mutagenicity assays, at concentrations of up to 5000 mcg/mL. In an in vivo micronucleus assay, no evidence of chromosomal damage to mouse bone marrow cells was observed following bolus intravenous doses of up to 118 mg/kg Herceptin.
A fertility study conducted in female cynomolgus monkeys at doses up to 25 times the weekly recommended human dose of 2 mg/kg trastuzumab and has revealed no evidence of impaired fertility, as measured by menstrual cycle duration and female sex hormone levels. Studies to evaluate the effects of trastuzumab on male fertility have not been conducted.
Animal Toxicology and/or Pharmacology
Reproductive Toxicology Studies
Reproductive toxicology studies have been conducted in cynomolgus monkeys at doses up to 25 times the weekly recommended human dose of 2 mg/kg Herceptin and have revealed no evidence of impaired fertility or harm to the fetus. However, HER2 protein expression is high in many embryonic tissues including cardiac and neural tissues; in mutant mice lacking HER2, embryos died in early gestation. Placental transfer of Herceptin during the early (Days 20—50 of gestation) and late (Days 120—150 of gestation) fetal development period was observed in monkeys.
Adjuvant Breast Cancer
The safety and efficacy of Herceptin in women receiving adjuvant chemotherapy for HER2 overexpressing breast cancer, were evaluated in an integrated analysis of two randomized, open‑label, clinical trials (Studies 1 and 2) with a total of 3752 women, a third randomized, open‑label, clinical trial (Study 3) with a total of 3386 women, and a fourth randomized, open‑label clinical trial with a total of 3222 patients (Study 4).
Studies 1 and 2
In Studies 1 and 2, breast tumor specimens were required to show HER2 overexpression (3+ by IHC) or gene amplification (by FISH). HER2 testing was verified by a central laboratory prior to randomization (Study 2) or was required to be performed at a reference laboratory (Study 1). Patients with a history of active cardiac disease based on symptoms, abnormal electrocardiographic, radiologic, or left ventricular ejection fraction findings or uncontrolled hypertension (diastolic > 100 mmHg or systolic > 200 mmHg) were not eligible.
Patients were randomized (1:1) to receive doxorubicin and cyclophosphamide followed by paclitaxel (AC→paclitaxel) alone or paclitaxel plus Herceptin (AC→paclitaxel + Herceptin). In both trials, patients received four 21‑day cycles of doxorubicin 60 mg/m2 and cyclophosphamide 600 mg/m2. Paclitaxel was administered either weekly (80 mg/m2) or every 3 weeks (175 mg/m2) for a total of 12 weeks in Study 1; paclitaxel was administered only by the weekly schedule in Study 2. Herceptin was administered at 4 mg/kg on the day of initiation of paclitaxel and then at a dose of 2 mg/kg weekly for a total of 52 weeks. Herceptin treatment was permanently discontinued in patients who developed congestive heart failure, or persistent/recurrent LVEF decline [ see Dosage and Administration (2.2) ]. Radiation therapy, if administered, was initiated after the completion of chemotherapy. Patients with ER+ and/or PR+ tumors received hormonal therapy. Disease‑free survival (DFS), defined as the time from randomization to recurrence, occurrence of contralateral breast cancer, other second primary cancer, or death, was the main outcome measure of the combined efficacy analysis.
A total of 3752 patients were included in the efficacy analyses. The data from both arms in Study 1 and two of the three study arms in Study 2 were pooled for efficacy analyses. Of these patients, the median age was 49 years (range, 22–80 years; 6% > 65 years), 84% were white, 7% black, 4% Hispanic, and 4% Asian/Pacific Islander. Disease characteristics included 90% infiltrating ductal histology, 38% T1, 91% nodal involvement, 27% intermediate and 66% high grade pathology, and 53% ER+ and/or PR+ tumors. At the time of randomization 53% of the population were to receive paclitaxel on a weekly regimen, and the remainder were to receive a q3 week schedule of paclitaxel.
In Study 3, breast tumor specimens were required to show HER2 overexpression (3+ by IHC) or gene amplification (by FISH) as determined at a central laboratory. Patients with node‑negative disease were required to have pathological tumor size ≥ T1c primary tumor. Patients with a history of congestive heart failure or LVEF <55%, uncontrolled arrhythmias, angina requiring medication, clinically significant valvular heart disease, evidence of transmural infarction on ECG, poorly controlled hypertension (systolic > 180 mm Hg or diastolic > 100 mm Hg) were not eligible.
Patients were randomized (1:1) upon completion of definitive surgery, and at least four cycles of chemotherapy; to receive no additional treatment (n = 1693) or 1 year of Herceptin treatment (n = 1693). Patients undergoing a lumpectomy had also completed standard radiotherapy. Patients with ER+ and/or PgR+ disease received systemic adjuvant hormonal therapy at investigator discretion. Herceptin was administered with an initial dose of 8 mg/kg followed by subsequent doses of 6 mg/kg once every three weeks for a total of 52 weeks. The main outcome measure was disease‑free survival (DFS), defined as in Studies 1 and 2.
Among the 3386 patients randomized to the two treatment arms, the median age was 49 years (range 21—80), 83% were Caucasian, and 13% were Asian. Disease characteristics: 94% infiltrating ductal carcinoma, 50% ER+ and/or PgR+, 57% node positive, 32% node negative, and in 11% of patients, nodal status was not assessable due to prior neo‑adjuvant chemotherapy. Ninety‑six percent (1055/1098) of patients with node‑negative disease had high risk features: among the 1098 patients with node‑negative disease, 49% (543) were ER− and PgR−, and 47% (512) were ER and/or PgR + and had at least one of the following high risk features: pathological tumor size greater than 2 cm, Grade 2—3, or age < 35 years. Prior to randomization, 94% of patients had received anthracycline‑based chemotherapy regimens.
In Study 4, breast tumor specimens were required to show HER2 gene amplification (FISH+ only) as determined at a central laboratory. Patients were required to have either node-positive disease, or node-negative disease with at least one of the following high-risk features: ER/PR-negative, tumor size > 2 cm, age < 35 years, or histologic and/or nuclear Grade 2 or 3. Patients with a history of CHF, myocardial infarction, Grade 3 or 4 cardiac arrhythmia, angina requiring medication, clinically significant valvular heart disease, poorly controlled hypertension (diastolic > 100 mmHg), any T4 or N2 or known N3 or M1 breast cancer were not eligible.
Patients were randomized (1:1:1) to receive doxorubicin and cyclophosphamide followed by docetaxel (AC‑T), doxorubicin and cyclophosphamide followed by docetaxel plus Herceptin (AC‑TH), or docetaxel and carboplatin plus Herceptin (TCH). In both the AC‑T and AC‑TH arms, doxorubicin 60 mg/m2 and cyclophosphamide 600 mg/m2 were administered every 3 weeks for four cycles; docetaxel 100 mg/m 2 was administered every 3 weeks for four cycles. In the TCH arm, docetaxel 75 mg/m2 and carboplatin (at a target AUC of 6 mg/mL/min as a 30‑ to 60‑minute infusion) were administered every 3 weeks for six cycles. Herceptin was administered weekly (initial dose of 4 mg/kg followed by weekly dose of 2 mg/kg) concurrently with either T or TC, and then every 3 weeks (6 mg/kg) as monotherapy for a total of 52 weeks. Radiation therapy, if administered, was initiated after completion of chemotherapy. Patients with ER+ and/or PR+ tumors received hormonal therapy. Disease free survival (DFS) was the main outcome measure.
Among the 3222 patients randomized, the median age was 49 (range 22 to 74 years; 6% ≥ 65 years). Disease characteristics included 54% ER+ and/or PR+ and 71% node positive. Prior to randomization, all patients underwent primary surgery for breast cancer.
Table 6: Efficacy Results from Adjuvant Treatment of Breast Cancer (Studies 1 + 2, Study 3, and Study 4)
| Studies 1 + 2
(0.54 – 0.84)
(0.48 – 0.76)
The results for DFS for the integrated analysis of Studies 1 and 2, Study 3, and Study 4 are presented in Table 7. The duration of DFS for Studies 1 and 2 is presented in Figure 4, and the duration of DFS for Study 4 is presented in Figure 5. Across all four studies, there were insufficient numbers of patients within each of the following subgroups to determine if the treatment effect was different from that of the overall patient population: patients with low tumor grade, patients within specific ethnic/racial subgroups (Black, Hispanic, Asian/Pacific Islander patients), and patients > 65 years of age.
| Figure 4 |
Duration of Disease‑Free Survival in Patients with Adjuvant Treatment of Breast Cancer (Studies 1 and 2)
| Figure 5 |
Duration of Disease‑Free Survival in Patient with Adjuvant Treatment of Breast Cancer (Study 4)
Exploratory analyses of DFS as a function of HER2 overexpression or gene amplification were conducted for patients in Studies 2 and 3, where central laboratory testing data were available. The results are shown in Table 8. The number of events in Study 2 was small with the exception of the IHC 3+/FISH+ subgroup, which constituted 81% of those with data. Definitive conclusions cannot be drawn regarding efficacy within other subgroups due to the small number of events. The number of events in Study 3 was adequate to demonstrate significant effects on DFS in the IHC 3+/FISH unknown and the FISH +/IHC unknown subgroups.
Table 7: Treatment Outcomes in Studies 2 and 3 as a Function of HER2 Overexpression or Amplification
| ||Study 2||Study 3|
|HER2 Assay ResultIHC by HercepTest, FISH by PathVysion (HER2/CEP17 ratio ≥ 2.0) as performed at a central laboratory.||Number of Patients||Hazard Ratio DFS (95% CI)||Number of Patients||Hazard Ratio DFS (95% CI)|
| FISH (+)||1170||0.42|
| FISH (−)||51||0.71|
| FISH Unknown||51||0.69|
|IHC < 3+ / |
|299All cases in this category in study 3 were IHC 2+.||0.53|
|IHC unknown / FISH (+)||—||—||724||0.59|
Metastatic Breast Cancer
The safety and efficacy of Herceptin in treatment of women with metastatic breast cancer were studied in a randomized, controlled clinical trial in combination with chemotherapy (Study 5, n=469 patients) and an open label single agent clinical trial (Study 6, n=222 patients). Both trials studied patients with metastatic breast cancer whose tumors overexpress the HER2 protein. Patients were eligible if they had 2 or 3 levels of overexpression (based on a 0 to 3 scale) by immunohistochemical assessment of tumor tissue performed by a central testing lab.
Previously Untreated Metastatic Breast Cancer (Study 5)
Study 5 was a multicenter, randomized, open‑label clinical trial conducted in 469 women with metastatic breast cancer who had not been previously treated with chemotherapy for metastatic disease. Tumor specimens were tested by IHC (Clinical Trial Assay, CTA) and scored as 0, 1+, 2+, or 3+, with 3+ indicating the strongest positivity. Only patients with 2+ or 3+ positive tumors were eligible (about 33% of those screened). Patients were randomized to receive chemotherapy alone or in combination with Herceptin given intravenously as a 4 mg/kg loading dose followed by weekly doses of Herceptin at 2 mg/kg. For those who had received prior anthracycline therapy in the adjuvant setting, chemotherapy consisted of paclitaxel (175 mg/m2 over 3 hours every 21 days for at least six cycles); for all other patients, chemotherapy consisted of anthracycline plus cyclophosphamide (AC: doxorubicin 60 mg/m2 or epirubicin 75 mg/m2 plus 600 mg/m2 cyclophosphamide every 21 days for six cycles). Sixty five percent of patients randomized to receive chemotherapy alone in this study received Herceptin at the time of disease progression as part of a separate extension study.
Based upon the determination by an independent response evaluation committee the patients randomized to Herceptin and chemotherapy experienced a significantly longer median time to disease progression, a higher overall response rate (ORR), and a longer median duration of response, as compared with patients randomized to chemotherapy alone. Patients randomized to Herceptin and chemotherapy also had a longer median survival (see Table 8). These treatment effects were observed both in patients who received Herceptin plus paclitaxel and in those who received Herceptin plus AC; however the magnitude of the effects was greater in the paclitaxel subgroup.
Table 8: Study 5: Efficacy Results in First‑Line Treatment for Metastatic Breast Cancer
| ||Combined Results||Paclitaxel Subgroup||AC Subgroup|
| ||Herceptin + All Chemotherapy|
(n = 235)
(n = 234)
|Herceptin + Paclitaxel|
(n = 92)
(n = 96)
|Herceptin + AC
(n = 143)
(n = 138)
| Primary Endpoint |
| Median TTP(mos)
| 95% CI||7, 8||4, 5||5, 10||2, 4||7, 9||5, 7|
||< 0.0001||< 0.0001||0.002|
| Secondary Endpoints |
| Overall Response Rate ||45||29||38||15||50||38|
| 95% CI||39, 51||23, 35||28, 48||8, 22||42, 58||30, 46|
|| < 0.001|| < 0.001||0.10|
| Median Resp Duration (mos) ,||8.3||5.8||8.3||4.3||8.4||6.4|
| 25%, 75% quartile||6, 15||4, 8||5,11||4, 7||6, 15||4, 8|
| Med Survival (mos) ||25.1||20.3||22.1||18.4||26.8||21.4|
| 95% CI||22, 30||17, 24||17, 29||13, 24||23, 33||18, 27|
Data from Study 5 suggest that the beneficial treatment effects were largely limited to patients with the highest level of HER2 protein overexpression (3+) (see Table 9).
Table 9: Treatment Effects in Study 5 as a Function of HER2 Overexpression or Amplification
|HER2 Assay Result||Number of Patients|
for Time to Disease Progression|
|Relative Risk for Mortality|
|CTA 2+ or 3+||469||0.49 (0.40, 0.61)||0.80 (0.64, 1.00)|
| FISH (+)
||325||0.44 (0.34, 0.57)||0.70 (0.53, 0.91)|
| FISH (−)||126||0.62 (0.42, 0.94)||1.06 (0.70, 1.63)|
|CTA 2+||120||0.76 (0.50, 1.15)||1.26 (0.82, 1.94)|
| FISH (+) ||32||0.54 (0.21, 1.35)||1.31 (0.53, 3.27)|
| FISH (–)||83||0.77 (0.48, 1.25)||1.11 (0.68, 1.82)|
|CTA 3+||349||0.42 (0.33, 0.54)||0.70 (0.51, 0.90)|
| FISH (+)||293||0.42 (0.32, 0.55)||0.67 (0.51, 0.89)|
| FISH (–)||43||0.43 (0.20, 0.94)||0.88 (0.39, 1.98)|
Previously Treated Metastatic Breast Cancer (Study 6)
Herceptin was studied as a single agent in a multicenter, open‑label, single‑arm clinical trial (Study 6) in patients with HER2 overexpressing metastatic breast cancer who had relapsed following one or two prior chemotherapy regimens for metastatic disease. Of 222 patients enrolled, 66% had received prior adjuvant chemotherapy, 68% had received two prior chemotherapy regimens for metastatic disease, and 25% had received prior myeloablative treatment with hematopoietic rescue. Patients were treated with a loading dose of 4 mg/kg IV followed by weekly doses of Herceptin at 2 mg/kg IV.
The ORR (complete response+partial response), as determined by an independent Response Evaluation Committee, was 14%, with a 2% complete response rate and a 12% partial response rate. Complete responses were observed only in patients with disease limited to skin and lymph nodes. The overall response rate in patients whose tumors tested as CTA 3+ was 18% while in those that tested as CTA 2+, it was 6%.