Breast cancer is the most common malignancy in women of the Western world. One prominent feature of breast cancer is the co-and overexpression of HER2 and protein tyrosine kinase 6 (PTK6). According to the current clinical cancer therapy guidelines, HER2-overexpressing tumors are routinely treated with trastuzumab, a humanized monoclonal antibody targeting HER2. Approximately, 30% of HER2-overexpressing breast tumors at least initially respond to the anti-HER2 therapy, but a subgroup of these tumors develops resistance shortly after the administration of trastuzumab. A PTK6-targeted therapy does not yet exist. Here, we show for the first time that the simultaneous knockdown in vitro, compared with the single knockdown of HER2 and PTK6, in particular in the trastuzumab-resistant JIMT-1 cells, leads to a significantly decreased phosphorylation of crucial signaling proteins: mitogen-activated protein kinase 1/3 (MAPK 1/3, ERK 1/2) and p38 MAPK, and (phosphatase and tensin homologue deleted on chromosome ten) PTEN that are involved in tumorigenesis. In addition, dual knockdown strongly reduced the migration and invasion of the JIMT-1 cells. Moreover, the downregulation of HER2 and PTK6 led to an induction of p27, and the dual knockdown significantly diminished cell proliferation in JIMT-1 and T47D cells. In vivo experiments showed significantly reduced levels of tumor growth following HER2 or PTK6 knockdown. Our results indicate a novel strategy also for the treatment of trastuzumab resistance in tumors. Thus, the inhibition of these two signaling proteins may lead to a more effective control of breast cancer.

Leptomeningeal carcinomatosis represents a rare manifestation of metastatic breast cancer (MBC). We herewith report on a patient suffering from HER2 overexpressing MBC who received intrathecal methotrexate and trastuzumab for meningeal carcinomatosis. A 48-year-old woman was diagnosed with breast cancer in December 2002. Following surgery, six cycles of adjuvant FE100C plus irradiation and, subsequently for 1 year, trastuzumab were given. As a result of disseminated metastatic spread in October 2005, the patient received whole-brain radiotherapy for symptomatic central nervous system involvement, and was put on several trastuzumab-based combination regimens (capecitabine, vinorelbine, paclitaxel). In June 2006, the patient developed clinical signs of terminal cone involvement with overflow incontinence and paraparesis of the legs. Immediate radiation led to partial relief from clinical symptoms. Subsequently, the patient was put on the tyrosine kinase inhibitor lapatinib and capecitabine (August to October 2007), but on November 6th the patient suffered again from overflow incontinence and weakness of the legs. Failing to respond to lapatinib, the patient received gemcitabine/cisplatin and, additionally, was recommenced on intravenous trastuzumab. Owing to progressive leptomeningeal disease, the patient received repeated doses of intrathecal methotrexate and trastuzumab. Within 2 weeks and four intrathecal treatments, cerebrospinal fluid cytology showed the absence of tumor cells. Moreover, a striking clinical improvement with resolution of the paraparesis of the legs and overflow incontinence was observed. This case report gives details regarding the clinical course of a breast cancer patient who received intrathecal trastuzumab and methotrexate via lumbar puncture for meningeal carcinomatosis of HER2-overexpressing MBC.

The prognostic and/or predictive value of the cancer biomarkers, urokinase-type plasminogen activator (uPA) and its inhibitor (plasminogen activator inhibitor [PAI]-1), determined by ELISA in tumor-tissue extracts, was demonstrated for several cancer types in numerous clinically relevant retrospective or prospective studies, including a multicenter breast cancer therapy trial (Chemo-N0). Consequently, for the first time ever for any cancer biomarker for breast cancer, uPA and PAI-1 have reached the highest level of evidence, level-of-evidence-1. At present, two other breast cancer therapy trials, NNBC-3 and Plan B, also incorporating uPA and PAI-1 as treatment-assignment tools are in effect. Furthermore, small synthetic molecules targeting uPA are currently in Phase II clinical trials in patients afflicted with advanced cancer of the ovary, breast or pancreas.