To be eligible for this study, patients were required to have a histologically confirmed diagnosis of MBC, in addition to at least one measurable lesion. All patients were ≥18 years and were required to have previously treated with anthracycline and taxane-based chemotherapy. Only patients with an Eastern Cooperative Oncology Group (ECOG) performance status of grade 0-2 were enrolled in this study. Adequate bone marrow function (an absolute neutrophil count ≥1,500×10³/µL and a platelet count ≥100,000×10³/µL), adequate renal function (a serum creatinine level ≤1.5 mg/dL), and adequate hepatic function (aspartate aminotransferase and alanine aminotransferase levels ≤3×upper limit of normal and a total bilirubin level ≤1.5×upper limit of normal) were required for the patients enrolled in this study. Patients were also required to have a left ventricular ejection fraction (LVEF) of ≥50%. Patients were allowed to have received prior adjuvant chemotherapy (including taxane- or anthracycline-containing regimens), as long as chemotherapy was received ≥6 weeks prior to entry into the study. Patients were also allowed to have received adjuvant trastuzumab if the final dose was received ≥12 months prior to study entry.

Patients were ineligible if they had local relapse only, tumor in the contralateral breast only, symptoms of brain metastases or leptomeningeal involvement, peripheral neuropathy of at least grade 2 (according to National Cancer Institute Common Toxicity Criteria, NCI-CTC) or serious conditions including cardiac disease, symptomatic dyspnea, uncontrolled hypercalcemia, or clinically relevant active infection. Patients were also excluded if they were pregnant or breast-feeding, had participated in another clinical trial within 30 days prior to inclusion in this study, had a history of another malignancy, except for adequately treated basal cell carcinoma of the skin or in situ cervical carcinoma, or previously exposed to trastuzumab or lapatinib. All patients provided informed consent, and this study was approved by the Institutional Review Board of Dong-A University Medical Center (No.11-32).

A primary antibody directed against HER2 (Neo Markers, Fremont, USA) was used. Patients overexpressing HER2 at the 3+ level of IHC staining were immediately eligible for inclusion. HER2 expression at the 2+ level required confirmation by HER2 gene amplification using fluorescent in situ hybridization (FISH) with PathVision® HER2 DNA probe kit (Vysis Inc., Downers Grove, USA). HER2 testing was conducted on a primary tumor sample or a biopsy from the metastatic site.

The patients were treated with 25 mg/m² of vinorelbine (over a 15-minute infusion period) on days 1 and 8, at 3-week intervals. The vinorelbine dose was adjusted each week on the day of therapy, based on hematological and/or non-hematological toxicity. Adjustments were made in the dose of vinorelbine (25% dose reduction) in patients who experienced grade ≥3 hematological toxicity, grade 4 febrile neutropenia, grade 4 neutropenia persisting for 7 days, or grade 4 thrombocytopenia. The granulocyte colony stimulating factor was used for cases in which treatment was delayed for more than 2 weeks because of neutropenia or febrile neutropenia. One-week delays in vinorelbine dosing were applied in cases of grade 2 or higher neutropenia and thrombocytopenia. The vinorelbine dosage was reduced by 25% in cases of grade 2 neurologic toxicity, until it resolved to grade 1 or lower. In cases of non-hematologic grade 3, vinorelbine administration was delayed until the side effects were resolved to grade 1 or lower. If toxicity persisted for more than 3 weeks, patients were dismissed from the study, as were patients with grade 4 non-hematologic toxicity.

Trastuzumab was administered at an initial dose of 4 mg/kg over 90 minutes, and was subsequently administered at weekly doses of 2 mg/kg (over a 30-minute period). If patients experienced an infusion syndrome characterized by rigor, fever, or other symptoms of hypersensitivity to trastuzumab, treatment was halted, and patients were assessed and treated with supportive measures (acetaminophen, diphenhydramine, H₂ antagonists, dexamethasone, or meperidine) as needed. Treatment was reinstituted when vital signs stabilized. The study protocol did not include dose adaptations or delays for trastuzumab. All patients received electrocardiograms and LVEF measurements upon enrollment, and every 9 weeks thereafter or more frequently when dictated by clinical circumstances. Trastuzumab application was paused when LVEF was reduced by >20% from baseline or was reduced to >10% below the lower limit of normal. If a reevaluation conducted after 1 month reflected stabilized cardiac function, trastuzumab treatment was resumed, albeit accompanied by short-term controls. Otherwise, trastuzumab treatment was halted. Trastuzumab was immediately halted in New York Heart Association (NYHA) III or IV cardiac dysfunction. Vinorelbine and trastuzumab were administered until disease progression, unacceptable toxicity, or patient refusal.

A physical examination, complete blood counts, blood chemistry, and chest X-rays were acquired after each cycle. Computed tomography scans were repeated every three cycles or earlier for cases in which clinical deterioration was detected. The primary endpoint of this study was the tumor response rate, and the secondary endpoints included the time to progression (TTP), overall survival (OS), and toxicities. Patients who had been treated with at least two cycles of therapy were assessable for response; all patients who received treatment were assessable for toxicity.

Tumor responses were evaluated using the Response Evaluation Criteria in Solid Tumors criteria. A complete response (CR) was defined as the disappearance of all measurable lesions for a minimum duration of 8 weeks. Partial response (PR) was defined as a reduction of 30% or more in the sum of products of the greatest diameters of measurable lesions, no increase in lesion size, and no new lesions. Stable disease (SD) was defined as a reduction of less than 30% and an increase of less than 20% without any appearance of new lesions. Progressive disease (PD) was defined as an increase of greater than 20% in tumor size or the appearance of new lesions. Toxicity was evaluated using the NCI-CTC criteria (version 3.0), and was recorded per patient as the worst episode that appeared during a treatment cycle.

This trial was designed to detect a response rate of 35%, as compared to a minimal clinically meaningful response rate of 20%. The two-stage optimal design devised by Simon was adopted, with a statistical power of 80% to accept the hypothesis and 5% significance to reject it. Allowing for a follow-up loss rate of up to 10%, the total required sample size was 31 patients with measurable disease. The TTP and the OS were calculated from treatment initiation to the initial observation of disease progression or death, respectively. The Kaplan-Meier method was applied to estimate overall and progression-free survival outcomes. No multivariate analyses were conducted, due to the limited sample size. All data were analyzed with SPSS software version 14.0 (SPSS Inc., Chicago, USA).

Between August 2004 and August 2008, 33 patients with MBC, who were pretreated with anthracycline and taxane-based therapy, were scheduled for treatment at the Dong-A University Medical Center, Busan, South Korea. The characteristics of the 33 patients enrolled in this study are described in Table 1. The median patient age was 53 years (range, 39-72 years). The performance status (ECOG) was grade 0-1 in the majority of the patients; three patients (9.1%) were grade 2.

Estrogen receptor (ER) expression was positive in 20 patients (60.6%) and progesterone receptor (PR) expression was positive in 22 patients (66.7%). All patients with hormone receptor-positive tumors had received adjuvant hormonal therapy, but only six of the 22 patients (27.3%) had previously received palliative hormonal therapy. Twenty-nine of the patients (88%) were +3 overexpression of HER-2 IHC, four possessed tumors with +2 overexpression and were FISH-positive.

One organ was involved in 18 patients (54.5%), two organs were involved in nine (27.3%) and three or more organs were involved in six (18.2%). The lung was the most common metastatic site (13 patients, 39.4%), and bone (12 patients, 36.4%), lymph nodes (ten patients, 30.3%), liver (nine patients, 27.2%) and skin and soft tissue (five patients, 15.2%) were involved in a combined fashion. Fifteen patients (45.5%) received vinorelbine plus trastuzumab treatment as a third-line chemotherapy, nine patients (27.3%) as a fourth-line, and nine patients (27.3%) as a fifth (or more)-line therapy. Enrolled patients were previously treated with doxorubicin and cyclophosphamide, paclitaxel or docetaxel, capecitabine, and gemcitabine. None of the patients received prior adjuvant or metaststic setting.

Of the 33 patients who were assessed for responses, PR was noted in ten patients (30.3%; 95% confidence interval [CI], 23-37%), SD was detected in 12 patients (36.4%), and PD was observed in 11 patients (33.3%). The response rate of third line treatment was not better than that of later line therapy (46.7% vs. 16.7%, p=0.062). The median follow-up duration was 12.9 months. The median TTP was 6.8 months (95% CI, 5.3-8.2 months) (Figure 1). The median OS was 12.4 months (95% CI, 10.3-14.6 months) (Figure 2). The OS of third line therapy tended to be longer than that of later line therapy, but the difference was not significant (13.5 vs. 8.9 months, p=0.192). At the time of study analysis, four patients remained in treatment, and 29 patients had discontinued the study. Twenty-seven patients had experienced tumor progression. Of those patients with PD, four (12.1%) were discovered to have new central nervous system metastases as sites of disease progression. An additional two patients withdrew their consent for physician or patient preference.

A total of 194 treatment cycles were administered to 33 patients, with a median number of three cycles (range, 2-12 cycles). The number of dose-reduced cycles was 74 (38.1%) among the 194 cycles. The reasons for dose reduction were neutropenia and/or febrile neutropenia. The relative dose intensities were 15 mg/m²/wk (90.6%) for vinorelbine and 1.9 mg/kg/wk (95.0%) for trastuzumab.

The incidence and severity of acute toxicity associated with combined vinorelbine and trastuzumab therapy was quite low. All treatment-related toxicities noted in this study are shown in Table 2. Grade 3 or 4 neutropenia was observed in 14 cycles of treatment (7.2%), but only three episodes of non-fatal neutropenic fever were detected. Grade 1 or 2 vomiting was noted in five patients (15.2%), and grade 1 or 2 peripheral sensory neuropathy was detected in two patients (6.1%). Many of the women with neuropathy had pre-existing symptoms from previous taxane-based treatments. Fewer than one-third of patients showed any alopecia, and the observed gastrointestinal symptoms were also mild, with less than 10% of patients exhibiting grade 2 constipation and no patients exhibiting grade 3 or 4 gastrointestinal toxicities. Notably, no case of congestive heart failure or asymptomatic reductions in LVEF ≥20% occurred in the study population. Additionally, no treatment-related deaths occurred during this study.