percentage of us who develop brain mets???

[Jackie07]

According to this Italian retrospective (2004-2007)study, 5% of Her2-positive breast cancer patients who were initially diagnosed at Stage I-III developed brain mets in a 4.1 year (average) span (while the brain mets incidents of Her2-negative patients was just 1.3%) :


Cancer. 2011 May 1;117(9):1837-46. doi: 10.1002/cncr.25771. Epub 2010 Nov 10.
Multifactorial central nervous system recurrence susceptibility in patients with HER2-positive breast cancer: epidemiological and clinical data from a population-based cancer registry study.

Musolino A, Ciccolallo L, Panebianco M, Fontana E, Zanoni D, Bozzetti C, Michiara M, Silini EM, Ardizzoni A.
Source

Medical Oncology Unit and Cancer Registry of Parma Province, University Hospital of Parma, Parma, Italy. antoninomusolino@hotmail.com

Abstract

BACKGROUND:

A series of retrospective studies have reported that patients with human epidermal growth factor receptor 2(HER2)-positive breast cancer are at a greater risk of central nervous system (CNS) metastases. Trastuzumab, which does not cross the blood-brain barrier, has been associated with this increased risk.
METHODS:

The authors evaluated incidence, survival, and risk factors for CNS metastases in the incident breast cancer population systematically collected by the Parma Province Cancer Registry over the 4-year period between 2004 and 2007.
RESULTS:

A total of 1458 patients with a diagnosis of stage I to III invasive breast cancer were analyzed for study purposes. At a median follow-up of 4.1 years, CNS events were observed in 1.3% and 5% of HER2-negative patients and HER2-positive patients, respectively (P < .0001). The administration of trastuzumab either as adjuvant therapy or for metastatic disease was associated with a significantly increased risk of CNS involvement at first disease recurrence and after first extracranial recurrence, respectively. According to multivariate analysis, HER2-positive status and trastuzumab treatment, high Ki-67 index, and hormone receptor negativity remained independent risk factors for the development of CNS metastasis.
CONCLUSIONS:

To the authors' knowledge, this is the first population-based cancer registry study analyzing factors associated with CNS recurrence in a general population of newly diagnosed breast cancer patients with known HER2 status. The data from the current study provide evidence that patients with HER2-positive breast cancer have a significantly higher incidence of CNS metastasis after treatment with trastuzumab. Improvements in systemic control and overall survival associated with trastuzumab-based therapy may lead to an "unmasking" of CNS disease recurrence that would otherwise remain clinically silent before a patient's death.
Copyright © 2010 American Cancer Society.

[Jackie07]

This study done by the Chinese has a good explanation of why Herceptin(Trastuzumab) seems to be linked to higher incidence of brain mets:

PLoS One. 2011;6(6):e21030. Epub 2011 Jun 9.
Trastuzumab in the Adjuvant Treatment of HER2-Positive Early Breast Cancer Patients: A Meta-Analysis of Published Randomized Controlled Trials.

Yin W, Jiang Y, Shen Z, Shao Z, Lu J.
Source

Department of Breast Surgery, Fudan University Shanghai Cancer Center, Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China.

Abstract

BACKGROUND:

Adjuvant trastuzumab therapy has yielded conflicting results for overall survival, concerns about central nervous system (CNS) metastasis, and questions about optimal schedule. Therefore, we carried out a meta-analysis to assess the benefits of concurrent or sequential trastuzumab with adjuvant chemotherapy for early breast cancer patients with HER2-positive tumors.
METHODS:

Computerized and manual searches were performed to identify randomized clinical trials comparing adjuvant chemotherapy with or without trastuzumab in HER2-positive early breast cancer patients. Odds ratios were used to estimate the association between the addition of trastuzumab to adjuvant chemotherapy and various survival outcomes. The fixed-effects or random-effects model was used to combine data.
FINDINGS:

With six eligible studies identified, this analysis demonstrated that patients with HER2-positive breast cancer derived benefit in disease-free survival, overall survival, locoregional recurrence and distant recurrence (all P<0.001) from the addition of trastuzumab to adjuvant chemotherapy, whereas trastuzumab did worse in CNS recurrence as compared to the control group (P = 0.018). Furthermore, concomitant use of trastuzumab significantly lowered the hazard of death (P<0.001) but bore a higher incidence of CNS recurrence (P = 0.010), while statistical significance failed to be discerned for either overall survival (P = 0.069) or CNS metastasis (P = 0.374) between the sequential and observation arms.
CONCLUSION:

This analysis verifies the efficacy of trastuzumab in the adjuvant setting. Additionally, our findings indirectly corroborate the superiority of concurrent trastuzumab to sequential use and also illuminate that prolonged survival is the possible reason for the higher incidence of CNS with trastuzumab versus observation.