Background: Monoclonal antibodies (mAb), such as trastuzumab are a valuable addition to breast cancer therapy. Data obtained from neoadjuvant settings revealed that antibody-dependent cell-mediated cytotoxicity (ADCC) is a major mechanism of action for the mAb trastuzumab. Conflicting results still call into question whether disease progression, prolonged treatment or concomitant chemotherapy influences ADCC and related immunological phenomena.Methods: We analyzed the activity of ADCC and antibody-dependent cell-mediated phagocytosis (ADCP) of peripheral blood mononuclear cells (PBMCs) from human epidermal growth factor receptor 2 (HER2/neu) positive breast cancer patients receiving trastuzumab therapy either in an adjuvant (n = 13) or metastatic (n = 15) setting as well as from trastuzumab treatment-naive (t-naive) HER2/neu negative patients (n = 15). PBMCs from healthy volunteers (n = 24) were used as controls. ADCC and ADCP activity was correlated with the expression of antibody binding Fc-gamma receptor (FcγR)I (CD64), FcγRII (CD32) and FcγRIII (CD16) on CD14+ (monocytes) and CD56+ (NK) cells, as well as the expression of CD107a+ (LAMP-1) on CD56+ cells and the total amount of CD4+CD25+FOXP3+ (T_reg) cells. In metastatic patients, markers were correlated with progression-free survival (PFS).Results: ADCC activity was significantly down regulated in metastatic, adjuvant and t-naive patient cohorts as compared to healthy controls. Reduced ADCC activity was inversely correlated with the expression of CD107a on CD56+ cells in adjuvant patients. ADCC and ADCP activity of the patient cohorts were similar, regardless of treatment duration or additional chemotherapy. PFS in metastatic patients inversely correlated with the number of peripheral T_regcells.Conclusion: The reduction of ADCC in patients as compared to healthy controls calls for adjuvant strategies, such as immune-enhancing agents, to improve the activity of trastuzumab. However, efficacy of trastuzumab-specific ADCC and ADCP appears not to be affected by treatment duration, disease progression or concomitant chemotherapy. This finding supports the application of trastuzumab at any stage of the disease.

Brain metastases (BM) are frequently diagnosed in patients with HER-2-positive metastatic breast cancer; in addition, an increasing incidence was reported for triple-negative tumours. We aimed to compare brain metastases free survival (BMFS) of breast cancer subtypes in patients treated between 1996 until 2010. Brain metastases free survival was measured as the interval from diagnosis of extracranial breast cancer metastases until diagnosis of BM. HER-2 status was analysed by immunohistochemistry and reanalysed by fluorescent in situ hybridisation if a score of 2+ was gained. Oestrogen-receptor (ER) and progesterone-receptor (PgR) status was analysed by immunohistochemistry. Brain metastases free survival curves were estimated with the Kaplan–Meier method and compared with the log-rank test. Data of 213 patients (46 luminal/124 HER-2/43 triple-negative subtype) with BM from breast cancer were available for the analysis. Brain metastases free survival differed significantly between breast cancer subtypes. Median BMFS in triple-negative tumours was 14 months (95% CI: 11.34–16.66) compared with 18 months (95% CI: 14.46–21.54) in HER-2-positive tumours (P=0.001) and 34 months (95% CI: 23.71–44.29) in luminal tumours (P=0.001), respectively. In HER-2-positive patients, co-positivity for ER and HER-2 prolonged BMFS (26 vs 15 m; P=0.033); in luminal tumours, co-expression of ER and PgR was not significantly associated with BMFS. Brain metastases free survival in patients with lung metastases was significantly shorter (17 vs 21 months; P=0.014). Brain metastases free survival in triple-negative breast cancer, as well as in HER-2-positive/ER-negative, is significantly shorter compared with HER-2/ER co-positive or luminal tumours, mirroring the aggressiveness of these breast cancer subtypes.

Recently, HER3-expression was postulated as independent risk factor for metastatic spread. Therefore, we investigated the role of HER3 expression as prognostic marker in metastatic breast cancer patients. Patients of different breast cancer subtypes diagnosed with metastatic disease (visceral and/or brain metastases) were identified from a breast cancer database. Tissue samples of the respective primary tumors were retrieved, and immunohistochemical staining for estrogen-receptor, progesterone-receptor, HER2, and HER3 was performed. In HER2 equivocal and selected HER3 positive cases, subsequent fluorescent in situ hybridization (FISH) analysis was performed. Tissue specimens of 110 patients were available for this analysis. 21% had strong, complete, membranous HER3 staining of at least 10% of all tumor cells; HER3 protein expression was not associated with HER3 gene amplification. HER2/HER3 co-overexpression was observed in 12/110 (11%) specimens and HER3-overexpression showed a statistically significant association with HER2-overexpression (p = 0.02). No correlation was observed for HER3-overexpression and overall survival (OS), time to diagnosis of brain metastases, and incidence of brain metastases. Still, in patients with HER3 overexpression, a higher rate of 'brain only' metastatic behavior was observed (p = 0.042). In the HER2-positive subgroup, HER3-overexpression was significantly associated with shorter OS from diagnosis of metastatic disease (median 17 vs. 35 months; p = 0.04; log rank test). HER2/HER3 co-overexpression is significantly associated with impaired OS from diagnosis of metastatic disease in patients with HER2-positive metastatic breast cancer. Co-inhibition of HER2 and HER3 or the inhibition of HER2/HER3 hetero-dimerization may improve clinical outcome in this subgroup.

Background: Brain metastases (BM) are a devastating complication of HER2-positive metastatic breast cancer (BC) and treatment strategies providing optimized local and systemic disease control are urgently required. The antibody-drug conjugate trastuzumab deruxtecan (T-DXd) improved progression-free survival (PFS) and overall survival (OS) over trastuzumab emtansine but data regarding intracranial activity is limited. In the primary outcome analysis of TUXEDO-1, a high intracranial response rate (RR) was reported with T-DXd. Here, we report the final PFS and OS results. Patients and Methods: TUXEDO-1 accrued adult patients with HER2-positive BC and active BM (newly diagnosed or progressing) without indication for immediate local therapy. The primary endpoint was intracranial RR; secondary endpoints included PFS, OS, safety, quality-of-life (QoL), and neurocognitive function. PFS and OS were estimated with the Kaplan-Meier method and analyzed in the per-protocol population. Results: At 26.5 months median follow-up, median PFS was 21 months (95% CI: 13.3–n.r.) and median OS was not reached (95% CI: 22.2–n.r.). With longer follow-ups, no new safety signals were observed. The most common grade 3 adverse event was fatigue (20%). Grade 2 interstitial lung disease and a grade 3 symptomatic drop of left-ventricular ejection fraction were observed in one patient each. QoL was maintained over the treatment period. Conclusions: T-DXd yielded prolonged intra- and extracranial disease control in patients with active HER2-positive BC BM in line with results from the pivotal trials. These results support the concept of antibody-drug-conjugates as systemic therapy for active BM.

Combining trastuzumab and chemotherapy is standard in her2/neu overexpressing advanced breast cancer. It is not established however, whether trastuzumab treatment should continue after the failure of one earlier combination. In this trial, we report our experience with continued treatment beyond disease progression. Fifty-four patients, median age 46 years, range 25-73 years, were included. We analysed for time to tumour progression (TTP) for first, second and beyond second line treatment, response rates and overall survival. Median time of observation was 24 months, range 7-51. Response rates for first line treatment were 7.4% complete remission (CR), 35.2% partial remissions (PR), 42.6% stable disease > 6 months (SD) and 14.8% of patients experienced disease progression despite treatment (PD). Corresponding numbers for second line were 3.7% CR, 22.2% PR, 42.6% SD and 31.5% PD; numbers for treatment beyond second line (60 therapies, 33 pts 3rd line, 18 pts 4th line, 6 pts 5th line, 2 pts 6th line and 1 patient 7th line) were 1.7% CR, 28.3% PR, 28.3% SD and 41.6% PD respectively. Median TTP was 6 months (m) in the first line setting, and also 6 m for second line and beyond second line. An asymptomatic drop of left ventricular ejection fraction below 50% was observed in one patient. No case of symptomatic congestive heart failure was observed. The data presented clearly strengthen evidence that patients do profit from continued trastuzumab treatment. The fact that TTP did not decrease significantly from first line to beyond second line treatment is especially noteworthy. Still, randomized trials are warranted.