ROLE OF THE PATHOLOGIST IN BIOMARKER STUDIES

Cancer chemoprevention is defined as intervention by chemical agents p rior to invasion to inhibit or slow the carcinogenic process. Using su rrogate endpoint biomarkers in chemoprevention studies may reduce the size, length and cost of clinical prospective randomized trials in hig h-risk populations. Intermediate biomarkers are measurable alterations in the tissues at risk and include differentiation, genetic compositi on, biochemical expression, and proliferation. Assessment is possible because invasive epithelial neoplasms are known to begin as intraepith elial proliferations with a spectrum of cellular abnormalities extendi ng to carcinoma in situ. Genetic heterogeneity begins in the intraepit helial phase; a stochastic accumulation of genetic errors characterize s the progression of clonal evolution within the tumor through the pro cess of invasion and metastasis. Pathologic features associated with t his process include tumor classification as well as whether it is intr aepithelial or invasive. If the process is intraepithelial, the grade and extent of the intraepithelial lesion are reported. If the neoplasm is invasive, tumor size, extent, degree of differentiation (histologi c and nuclear grade), mitotic rate, vascular invasion, and lymph node involvement are evaluated. In assessing biomarkers relevant to chemopr evention, and without complete regression of the neoplasm with the che mopreventive agent or agents, measurable parameters along with histopa thologic features are applicable. Three methods readily applicable for this purpose that can be applied to paraffin-embedded, formalin-fixed tissue include quantitative pathology, immunohistochemistry, and mole cular biologic applications. These methods require some consistency in handling and processing the tissues under study; results may deterior ate due to a number of processing variables, including time to fixatio n, time in fixative, and fixative type. Quantitative pathology, includ ing static image analysis and flow cytometry, can determine total DNA content. Using static image analysis, very small tumors can be studied . In addition, adjacent intraepithelial and invasive components of a t umor may be studied from a single slide. Steroid receptors, oncogenes, and other proteins detectable through immunohistochemical or molecula r biologic methods can be quantitated by this technique as well. Cell cycle synthetic function is assayable by both methods. Flow cytometry can calculate the total percentage of cells in S-phase, or the tumor c ell S-phase fraction based on the percentage of cells detected between the G(0), G(1) peak and the G(2) + M peak. A similar approach is gene rally not applicable with current image analysis equipment; however, c ell cycle related proteins such as MIB-1 (Ki-67 associated) can be qua ntified. Immunohistochemical methods can employ a wide variety of mono clonal antibodies to detect oncogene related proteins, including HER-2 /neu (c-erbB-2) and p53. Molecular biologic methods, including in situ hybridization, polymerase chain reaction, and in situ PCR, can have m any applications when applied to paraffin-embedded tissues, including detection of viral DNA, identification and measurement of apoptosis, a nd defining gene deletions. (C) 1995 Wiley-Liss, Inc.