Chemoprevention of upper aerodigestive tract cancers: a report of the third Upper Aerodigestive Cancer Task Force workshop

The emerging role of retinoids and retinoic acid metabolism blocking agents in the treatment of cancer

BACKGROUND

Although significant advances have been made in the treatment of some malignancies, the prognosis of patients with metastatic tumors remains poor. Differentiating agents redirect cells toward their normal phenotype and therefore may reverse or suppress evolving malignant lesions or prevent cancer invasion. In addition, they offer a potential alternative to the classic cytostatic drugs.

METHODS

The purpose of this review was to examine the current and potential future roles of differentiating agents in the treatment of cancer.

RESULTS

Initial studies with differentiating agents focused on retinoid therapy. Although retinoids have shown some clinical success, their widespread use has been limited by resistance and, in the chemopreventive setting, toxicity. This has led to the synthesis of a number of new retinoids that currently are undergoing clinical investigation. A further approach to overcoming the drawbacks associated with exogenous retinoids has been to increase the levels of endogenous retinoic acid (RA) by inhibiting the cytochrome P450-mediated catabolism of RA using a novel class of agents known as retinoic acid metabolism blocking agents (RAMBAs). Liarozole, the first RAMBA to undergo clinical investigation, preferentially increases intratumor levels of endogenous RA resulting in antitumor activity.

CONCLUSIONS

Although studies using exogenous retinoids in this setting have not yet fulfilled their initial promise, studies with a growing set of synthetic retinoids are ongoing. Furthermore, modulation of endogenous retinoids may offer a significant new potential treatment for cancer.

Molecular and cellular biomarkers for field cancerization and multistep process in head and neck tumorigenesis

One way to explain the development of head and neck cancer is through the theories of field cancerization, i.e., the exposure of an entire field of tissue to repeated carcinogenic insult, and multistep process, i.e., development of multiple cancers in a predisposed filed through a series of recognizable stages. Recent molecular genetic studies of histologically normal and premalignant epithelia of high-risk subjects and studies of malignant tumors in aerodigestive tract epithelia have identified a continuum of accumulated specific genetic alterations that possibly occur during the clonal evolution of tumors, namely, during the multistep process. Second primary or multiple primary tumors arise in the same fields as independent clones, with similar but unique molecular genetic and/or cellular alterations. Consequently, the assessment of these genetic and phenotypic alterations has been integrated into clinical chemoprevention trials in an effort to identify biomarkers that are also risk predictors and intermediate end points. This review covers candidate biomarkers of the processes of field cancerization and multistep tumor development in aerodigestive tract epithelia, including general and specific genetic markers, proliferation markers, and squamous differentiation markers.

Early diagnosis and prevention of oral cancer and precancer: report of Symposium III

Oral precancer encompasses several conditions and lesions. Among those entities included in the concept are leukoplakia, erythroplakia, lichen planus, and submucous fibrosis. For prevention, knowledge about etiologic and pathogenetic factors is imperative. It is well-known that excessive consumption of tobacco and alcohol has a bearing on the development of oral leukoplakia and probably also of erythroplakia. However, among leukoplakias, the idiopathic or cryptogenic type probably shows the most serious malignant potential. Involved in the development of such lesions may be general nutritional aspects, e.g., proper utilization of vitamin A. It is also well-known that iron deficiency has been linked to Plummer-Vinson's syndrome, showing a precancerous trait. Among factors involved in the pathogenesis of lichen planus is probably mental stress. Thus, stress factors and related neurological components have been linked to the immunological system. Lifestyle factors, such as nutrition, tobacco, and alcohol, and also mental environment may be of importance for the development of oral precancer and cancer.

A panel of biomarkers of carcinogenesis of the upper aerodigestive tract as potential intermediate endpoints in chemoprevention trials

BACKGROUND

Patients with squamous cell carcinoma of the head and neck have a 10-30% risk of developing a second primary tumor. The concept of "field cancerization" assumes that the whole upper aerodigestive tract is affected and prone to malignant transformation. This study was undertaken to investigate the value of a panel of monoclonal antibodies to identify biomarkers in oral mucosa associated with cancer risk. Such biomarkers may be suitable candidates to serve as intermediate endpoints in cancer chemoprevention trials.

METHODS

As a model, the expression of antigens was assessed in cytologic preparations obtained from macroscopically normal oral mucosa of patients with tongue carcinoma and of controls. The panel consisted of antibodies against cytokeratin 8, 10, 13, and 19 and the monoclonal antibodies designated K931, K984, E48, Ki-67, and UM-A9.

RESULTS

Oral mucosa of cancer patients had a more than threefold increased expression of cytokeratin 19 as compared with controls (36.0 versus 11.3%; P < 0.01).

CONCLUSION

Cytokeratin 19 is a potential intermediate endpoint in head and neck cancer chemopreventive trials.

Detection and localization of early lung cancer by imaging techniques

Two new technologic developments may have a significant impact on the detection and localization of early lung cancer. These two developments work together in a complementary way. The first is a solid-state microscope that can be applied in the prescreening of sputum cytology specimens. The finding that malignancy-associated changes (MACs) are present in ostensibly normal bronchial epithelial cells may be used to improve the sensitivity of sputum cytology to detect cancer. Once abnormal or MAC cells are found, a second device, a fluorescence bronchoscope, can be employed to localize the source of the abnormal cells. Fluorescence bronchoscopy is also a potentially useful tool for procuring premalignant tissue for molecular biology studies and for monitoring the progress of patients in chemoprevention studies.

Markers of keratinocyte differentiation in snuff-induced leukoplakia

Biopsy specimens from 12 patients who used snuff and had leukoplakia in the mucosa of the oral cavity were studied and compared with specimens from their own nonleukoplakic oral mucosa, as well as with biopsy specimens from corresponding areas of the oral cavity in 12 nonsmoking, nontobacco-using control subjects. The biopsy specimens were processed using standard immunohistochemical rabbit antibody to human involucrin and mouse antibody to human transglutaminase type I as the primary antibodies. A computer-driven light absorbance image analysis system was used to determine the optical density of each of the marker-stained specimens. Optical density measurements were compared using a one-way analysis of variance. The expression of involucrin was significantly higher in the epithelium of the nonsmoking, nontobacco-using control subjects (0.2937 +/- 0.0725 optical density) in comparison with the normal-appearing mucosa (0.2283 +/- 0.0488 optical density) and the leukoplakic mucosa of the snuff-using patients (0.2007 +/- 0.0669 optical density) (p < 0.05). The expression of transglutaminase type I was also significantly higher in the epithelium of the nonsmoking, nontobacco-using controls (0.2308 +/- 0.1381 optical density) than in the patients with leukoplakic mucosa (0.1310 +/- 0.0472 optical density) (p < 0.05). However, there was no difference when compared with the normal-appearing mucosa of the patients in the snuff-using group (0.1686 +/- 0.0323 optical density). This study has shown that involucrin and transglutaminase type I are expressed differently in leukoplakic oral mucosa of snuff users and in normal oral mucosa and that this difference can be measured objectively.

The study of markers of biological effect in cancer prevention research trials

Biological markers may provide a valuable tool for the development of cancer prevention agents, for monitoring patient compliance to a selected intervention, or for further defining the carcinogenic process. This discussion focuses on markers of biological effect and the rationale for their use in cancer prevention trials. Recent studies with biological markers are investigating their incorporation into phase-I, -II, and -III chemoprevention clinical trial designs. Their use in clinical studies is expected to increase the number of agents that may be evaluated and to provide valuable information on the biological effectiveness of agents, doses, and schedules. Markers may also provide information to help in selecting high-risk groups for prevention research, and to indicate the pathways inhibited and the stage of carcinogenesis affected. Such information may prove of crucial importance in strengthening the rationale for long-term trials and other ancillary research. Biomarker research for colon carcinogenesis is discussed, including examples of a number of recent trials that may influence future progress in this area of prevention research. A crucial step in this process is marker validation as an aspect of major prospective observational and intervention studies where cancer incidence is the endpoint. We cannot be fully confident of markers as intermediate endpoints until the evidence from clinical trials is sufficiently strong to support major public health initiatives for prevention.

Bronchial micronuclei as a marker of an early stage of carcinogenesis in the human tracheobronchial epithelium

In the bronchial epithelium, smoking initiates a multistep process that first appears histologically as premalignant squamous metaplasia/dysplasia, a biological predecessor of squamous-cell lung cancer. Reflecting chromosomal damage from a carcinogenic insult, micronuclei may reveal earlier events in the carcinogenic sequence. We prospectively evaluated and correlated micronucleus count, histology (index of metaplasia) and smoking exposure in 35 consecutive subjects (9 active smokers, 10 previous smokers and 16 never-smokers) undergoing diagnostic bronchoscopy. Samples for micronuclei and histological evaluation were taken from the main carinal mucosa in each subject for site-specific comparisons. The median and mean micronucleus counts per 1,000 cells were significantly higher in active smokers than in non-smokers (subjects who had never smoked and previous smokers): median counts were 3.7 vs. 1.4, p = 0.03; mean counts were 4.7 vs. 1.9, p = 0.01. There was no significant difference, however, in micronucleus counts between subjects who had never smoked and previous smokers. Bronchial metaplasia and smoking history were not associated. Our findings suggest that micronuclei are a readily quantitated, early intermediate-endpoint marker for detecting tobacco-initiated tracheobronchial carcinogenesis.