Factors affecting treatment choice in HER2 positive metastatic breast cancer.

University of Minnesota Ph.D. dissertation. March 2009: Major: Nursing. Advisor: Cynthia Gross, PhD. 1 computer file (PDF); x, 129 pages, appendices 1-2.Women with HER2 positive breast cancer have decreased overall survival and may have a poorer response to treatment. Evidence suggests that disparities exist in treatment and outcomes in individuals with diverse racial and ethnic backgrounds, the elderly, individuals that are obese, hormone receptor positive, those with comorbid conditions, those treated in various regions of the country, and in different treatment settings. Trastuzumab (Herceptin®) is an anti-HER2 monoclonal antibody and was the first targeted therapy developed for the treatment of HER2 positive metastatic breast cancer. With its approval by the U.S. Federal Drug Administration in 1998, trastuzumab became the standard of care for treatment of HER2 positive MBC. This study examined differences in treatment, specifically trastuzumab use, and outcomes in these various groups treated for HER2 positive metastatic breast cancer. A conceptual framework guided by the fourth version of Andersen's health service utilization model was developed to better understand treatment patterns in these various groups. A prospective observational database called RegistHER was the source of the data. The first outcome evaluated was whether the frequency of use of optimal therapy (antibody) varied by group. Using logistic regression, this study showed no difference in use of optimal treatment in participants based on region of the country, race, obesity status or comorbid conditions. Differences in these groups might be seen given larger sample sizes. There were differences seen in individuals treated in different settings, the elderly, and those in that are ER/PR positive. Although women who are hormone receptor positive are eligible for treatment with hormones, consideration should be given to concurrent or sequential treatment with antibody therapy in those women that are HER2 positive. The second outcome evaluated was the time to start of treatment (in days). Logistic regression showed no variables were significant for this outcome indicating that race, age, obesity status, treatment setting, region of the country, hormone receptor status, the presence of cardiac disease and comorbid conditions did not affect time to start of treatment in this sample of patients from the RegistHER database. The third outcome evaluated was time to progression of disease. Using Cox regression, those who were ER/PR positive had a reduced risk of having progressive disease than their ER/PR negative counterparts. Not surprisingly, those with ER/PR positive disease did better than those that were ER/PR negative since those that have HR negative disease typically have a poorer prognosis than their HR positive counterparts. An unplanned sub-analysis showed that when you look at just those that are HR positive and compare those who got antibody to those that did not get antibody, both groups progressed at about the same rate. RegistHER, a registry with the largest cohort of HER2 positive MBC patients followed to date, is important because it provides a unique opportunity to characterize treatment patterns in this subset of individuals with breast cancer. In this evaluation of the database, important information regarding use of optimal treatment and time to progressive disease for women with HER2- positive breast cancer was described. Given the findings, this additional data may guide clinical decision-making for healthcare providers and their HER2 positive breast cancer patients and ultimately improve outcomes