Quantitation of p95HER2 in Paraffin Sections by Using a p95-Specific Antibody and Correlation with Outcome in a Cohort of Trastuzumab-Treated Breast Cancer Patients

Primary trastuzumab resistance: new tricks for an old drug

Trastuzumab is the first Food and Drug Administration (FDA)-approved therapeutic targeting a HER-family receptor tyrosine kinase (HER2/ErbB2/neu). Although trastuzumab is effective in the treatment of HER2-positive breast cancer, a substantial proportion of patients will not respond to trastuzumab-based regimens (primary resistance), and those who do respond will often lose clinical benefits (i.e., secondary resistance). Although multiple mechanisms underlying the development of secondary trastuzumab resistance have been identified, few studies have specifically examined the basis of primary trastuzumab resistance. Here, we review these studies, which together demonstrate that trastuzumab induces phenotypic changes in tumor cells, even when they are not growth inhibited by trastuzumab, including changes in gene expression. These changes have important clinical implications, including the sensitization of malignant cells to other therapeutic drugs. In light of these observations, we propose that the conventional definition of resistance as it pertains to trastuzumab and, perhaps, to other targeted therapeutics, may require revision. The results of these studies will be useful in informing the direction of future basic and clinical research focused on overcoming primary trastuzumab resistance.

Lapatinib: new opportunities for management of breast cancer

Approximately 20% of new diagnosed breast cancers overexpress the human epidermal growth factor receptor 2 (EGFR2), also known as erythroblastic leukemia viral oncogene homolog 2 (ERBB2) protein, as a consequence of ERBB2 gene amplification, resulting in a poor prognosis. Clinical outcome can be substantially improved by ERBB2-targeted therapy. Lapatinib is a potent, orally bioavailable small molecule that reversibly and selectively inhibits epidermal growth factor receptor (EGFR1 or ERBB1) and ERBB2 tyrosine kinases. Lapatinib binds the adenosine triphosphate-binding site of the receptor's intracellular domain to inhibit tumor cell growth. This review summarizes the pharmacology, pharmacokinetics, efficacy, and tolerability of lapatinib, and reviews both Food and Drug Administration-approved and investigational uses of lapatinib in breast cancer therapy. The drug is generally well tolerated in patients, with diarrhea and rashes being the most common (usually mild or moderate) adverse effects. Unlike trastuzumab, lapatinib has infrequent adverse effects on cardiac function. Lapatinib has substantial activity for advanced ERBB2-positive breast cancer, particularly in combination with capecitabine, following progression after anthracyclines, taxanes, and trastuzumab. Lapatinib combined with capecitabine yielded significant improvements in time to progression and response rate compared with capecitabine alone. This drug can also be combined with letrozole for the treatment of postmenopausal women with ERBB2-positive breast cancer, for whom hormonal therapy is indicated. Lapatinib has shown early promise in treatment of central nervous system metastasis and is being further evaluated in various clinical settings.

HER2 fragmentation and breast cancer stratification

HER2 is a tyrosine kinase receptor whose overexpression in breast cancers correlates with poor prognosis. A subset of HER2-positive tumors also expresses a series of HER2 fragments, collectively known as p95HER2. These fragments are emerging as a valuable biomarker for this subset of patients, who have a particularly poor prognosis.