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INTRODUCTION

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Breast cancer is a heterogeneous disease associated with differences in morphology, biology, and response to therapy. In order to characterize this heterogeneity, it is necessary to assess molecular markers that identify subclasses or stage of disease. The term biomarkers is used to define 'a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to therapeutic intervention' [1]. In patients with breast cancer, biomarkers are used in clinical practice in a number of situations, the most common being predictive or prognostic markers and rarely pharmacogenomic processes. Pharmacokinetic and pharmacodynamic markers, although common in the research setting, are seldom used in clinical practice (Table 2.1). The biomarkers may be assessed in tissues or body fluids, such as blood (including plasma, serum), urine, or cere-brospinal fluid, and may be DNA, RNA, proteins, or carbohydrates. Depending on which marker is being studied, there may be different conditions required for collecting and handling the specimens.

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Table 2.1Types of assay in clinical trials
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BODY FLUID-BASED BIOMARKERS

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Body fluid-based markers are obtained by minimal or non-invasive interventions and thus can be assessed serially or at multiple time points. In addition, the samples obtained can be quickly divided in to aliquots and stored or processed differently. The commonest examples of these are blood-derived assays, where the blood can be assessed as a whole sample or split into components such as plasma and serum. Depending on the assay, the samples can be collected under different conditions and with different preservatives. For example, blood might be allowed to clot (for collection of serum) or anticoagulate (for collection of plasma). As cellular components within the blood continue to degenerate, it is important to separate the components as quickly as possible to prevent contamination of the results and improve stability of the assay. Standard operative procedures for all aspects (preanalytical, analytical, and interpretational) of the assay can be devised and are relatively easy to follow.

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PREANALYTICAL FACTORS

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Preanalytical factors include all aspects of the assay process prior to the conduct of the assay itself. These include collection, preprocessing, and processing of the sample, including storage until the time of conduction of the assay.

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Sample collection
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The samples can be obtained in a standardized manner, including the time of the day and day of the week ...

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