Strategies for the application of biomarkers for risk assessment and efficacy in breast cancer chemoprevention trials

Potential roles of genetic biomarkers in colorectal cancer chemoprevention

Colorectal cancer is a significant cause of morbidity and mortality in industrialized societies and the second most frequent cause of cancer death in the United States. Surrogate endpoint biomarkers are gaining wide acceptance in early diagnosis and short-term cancer chemoprevention trials in place of cancer endpoints. Molecular genetic biomarkers can be useful tools in identifying subjects at risk of developing cancer and screening for early cancers amenable to complete cure. They may be useful both in predicting and assessing response to a given therapy and in determining prognosis after an initial diagnosis has been made. Ideally, biomarkers should fulfill some, if not all, of the following criteria: variability of expression between phases of carcinogenesis, association with cancer risk, ability to undergo modification in response to a chemopreventive agent, and finally, permit ease of measurement. In consideration of colorectal cancer chemoprevention, several genetic biomarkers seem to meet many of these criteria, as they do exhibit distinct variability of expression at different phases of carcinogenesis, are often strongly associated with increased cancer risk (especially the hereditary/familial syndromes), are generally able to be measured relatively easily through peripheral blood sampling (germline mutations) or by colonic mucosal sampling by endoscopic techniques (somatic mutations). In some cases, genetic biomarkers have also been demonstrated to undergo modification in response to a chemopreventive agent. With further understanding of the genetic and molecular changes involved in sporadic and familial colorectal carcinogenesis, genetic biomarkers appear to hold great potential for the identification of subjects at high risk of developing colorectal cancer, as well as the development of novel chemopreventive approaches and form a promising area for further research.

Genetic changes in breast cancer--consequences for therapy?

The knowledge of specific genetic changes and their biological consequences is critical to an understanding of the natural history of breast tumors and the development of rational means to prevent and treat them. A number of genetic changes have been identified in breast tumors. Some of these involve specific genetic loci that directly contribute to one or more attributes of transformation, i.e., dysregulated proliferation and invasion, while other changes confer genetic instability that increases the possibility of acquiring subsequent, specific genetic lesions relevant to tumorigenesis. Many of these changes have been correlated with an adverse prognosis and attempts to integrate these in comprehensive multifactorial prognostic models are in progress. Initial clinical trials have also demonstrated the 'proof of concept' of targeting specific genetic lesions for therapeutic purposes. In the not too distant future, we can envision the use of specific therapies for individual (or subgroups of) tumors based on the specific genetic changes that lead to their development, rather than the global approach of multiagent cytotoxic therapy that is in widespread use today.

A phase II chemoprevention trial design to identify surrogate endpoint biomarkers in breast cancer

Surrogate biomarkers for risk assessment and efficacy of potential chemopreventive agents are needed to improve the efficiency and reduce the cost of conducting chemoprevention trials. In addition to criteria of sensitivity, specificity, quantifiability, and reproducibility applicable to most potential biomarkers, there are additional specific constraints in developing biomarkers for specific organ sites. In the case of breast tissue, these difficulties include lack of a consensus on the nature of premalignant lesions and the histologic criteria used to define them; even when such a consensus can be evolved, there are limitations in visualizing such lesions without invasive biopsies. Also, knowledge of specific genetic and biochemical changes in premalignant lesions is limited. In addition, the physiology of breast tissue is cyclic, no proven, relevant markers can be studied in a randomly obtained needle aspirate. The earliest determinate lesion that can be recognized in breast tissue is ductal carcinoma in situ (DCIS). At the University of Texas M.D. Anderson Cancer Center, we have initiated a study to develop biomarkers for tamoxifen and 4-hydroxyphenylretinamide by administering one or both of these drugs to women with DCIS or small invasive lesions in the interval between the initial diagnostic core biopsy and definitive surgery. The treatment is to be administered for 2-4 weeks. Proposed biomarkers to be studied include: (a) markers associated with neoplastic phenotypes, e.g., excessive proliferation, alternations of nuclear morphology and angiogenesis; (b) proteins likely to be required for response to the putative chemopreventive agents, e.g., estrogen receptor, nuclear retinoid receptors; (c) markers indicative of intact downstream response pathways, e.g., progesterone receptors; (d) oncogenes and tumor suppressor genes regulated by the proposed chemopreventive agents, e.g., neu, TGF-beta; and (e) potential novel markers of genetic instability that could be studied in randomly obtained needle aspirates, i.e., random chromosomal gains and losses in high risk mammary epithelium. The experience gained in designing and conducting this trial is expected to facilitate development of future chemoprevention trials of breast, as well as other organ site cancers.

Role of the pathologist in biomarker studies

Cancer chemoprevention is defined as intervention by chemical agents prior to invasion to inhibit or slow the carcinogenic process. Using surrogate endpoint biomarkers in chemoprevention studies may reduce the size, length and cost of clinical prospective randomized trials in high-risk populations. Intermediate biomarkers are measurable alterations in the tissues at risk and include differentiation, genetic composition, biochemical expression, and proliferation. Assessment is possible because invasive epithelial neoplasms are known to begin as intraepithelial proliferations with a spectrum of cellular abnormalities extending to carcinoma in situ. Genetic heterogeneity begins in the intraepithelial phase; a stochastic accumulation of genetic errors characterizes the progression of clonal evolution within the tumor through the process of invasion and metastasis. Pathologic features associated with this process include tumor classification as well as whether it is intraepithelial 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 (histologic and nuclear grade), mitotic rate, vascular invasion, and lymph node involvement are evaluated. In assessing biomarkers relevant chemoprevention, and without complete regression of the neoplasm with the chemopreventive agent or agents, measurable parameters along with histopathologic 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 molecular biologic applications. These methods require some consistency in handling and processing the tissues under study; results may deteriorate due to a number of processing variables, including time to fixation, time in fixative, and fixative type. Quantitative pathology, including 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 tumor may be studied from a single slide. Steroid receptors, oncogenes, and other proteins detectable through immunohistochemical or molecular 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 cell S-phase fraction based on the percentage of cells detected between the G0, G1 peak and the G2 + M peak. A similar approach is generally not applicable with current image analysis equipment; however, cell cycle related proteins such as MIB-1 (Ki-67 associated) can be quantified. Immunohistochemical methods can employ a wide variety of monoclonal 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 many applications when applied to paraffin-embedded tissues, including detection of viral DNA, identification and measurement of apoptosis, and defining gene deletions.