chapter  9
Personalized Medicine by the Use of Microarray Gene Expression Profiling
ByStella Mook, Laura J. van ’t Veer, and Fatima Cardoso
Pages 12

For accurate management of early breast cancer, several important decisions

need to be made by patients and clinicians regarding the type of surgery, the

need for adjuvant radiotherapy, and particularly the type of adjuvant systemic

therapy (chemotherapy and/or endocrine therapy). The decision about adjuvant

systemic therapy is of paramount importance since breast cancer is mainly a

systemic disease, with a majority of deaths occurring as a consequence of distant

metastases. This decision depends on the likelihood of recurrence; patient-

related factors such as biological age, menopausal status, performance status,

and co-morbidities; and tumor-related factors such as size, grade, lymph node

status, and hormonal and human epidermal growth factor receptor 2 (HER2)

status. Most of these variables are combined into prognostic models or guidelines

such as the St. Gallen consensus or the National Comprehensive Cancer Network

(NCCN) guidelines, in order to assist patients and clinicians in the decision-

making process (1-3). Although these guidelines provide valuable information

about prognosis in certain breast cancer populations, the prediction of disease

outcome for the individual patient is far from accurate. In reality, patients with

similar clinicopathological characteristics can have strikingly different outcomes.

Because of these limitations, and because of the recognition of the incurable

nature of metastatic breast cancer, clinicians consider prescribing adjuvant

chemotherapy in the majority of early-stage breast cancer patients to reduce the

risk of relapse. However, a large proportion of these patients is probably cured

with locoregional treatment alone or in combination with adjuvant endocrine

therapy, thus unnecessarily exposing many patients to chemotherapy side effects.

The identification of robust and reliable prognostic markers that accurately select

patients not requiring adjuvant chemotherapy is essential to decrease the problem

of overtreatment. Additionally, a more accurate patient selection will also con-

tribute to the decrease in undertreatment, a less common but dangerous problem.