Persistence of genetically altered fields in head and neck cancer patients: biological and clinical implications.

In 1953, Slaughter et al. [D. P. Slaughter et al., Cancer (Phila.), 6: 963-968, 1953] proposed the concept of field cancerization in patients with squamous cell carcinoma of the head and neck (HNSCC) and discussed its clinical significance for the development of second primary tumors and local recurrences. To define the process of field cancerization and its putative clinical implications, we analyzed genetic aberrations in HNSCC and the accompanying macroscopically normal mucosa. In 28 HNSCC patients, loss of heterozygosity was determined in tumor and five noncontiguous mucosal biopsies using eight microsatellite markers at 9p, 3p, and 17p. For patients who showed loss of heterozygosity in their mucosal biopsies, all margins of the surgical specimen were subsequently analyzed to determine the extension of the field. In these cases, additional markers at 8p, 13q, and 18q as well as p53 mutations were included to determine subclonal differences between field and tumor. Genetically altered fields were detected in 36% (10 of 28) of the HNSCC patients. The field varied in size between patients and consisted of genetically different subclones. In 7 of 10 cases, the field extended into the surgical margins. One particular patient with a genetically altered field in a surgical margin developed a local recurrence after 28 months of follow-up. Microsatellite analysis showed that this recurrence had more molecular markers in common with the nonresected premalignant field than with the original tumor, suggesting that this persistent field has progressed further into a new malignancy. Our data show that genetically altered mucosa remains after treatment in a significant proportion of HNSCC patients, which may explain in part the high frequency of local recurrences and second primary tumors. Adequate identification and risk assessment of these genetically altered fields may have profound implications for future patient management.

Molecular assays for the diagnosis of minimal residual head-and-neck cancer: methods, reliability, pitfalls, and solutions.

The prognosis of cancer patients is determined by the radicalness of treatment: residual tumor cells will grow out and develop in manifest local recurrences, regional recurrences, and distant metastases. Classical diagnostic methods such as radiology and histopathology have limited sensitivities, and only by molecular techniques can minimal residual disease be detected. In tissue samples containing the normal tissue counterpart of a tumor, only tumor-specific markers can be exploited, whereas in other samples, tissue-specific markers can be used. At present, there are two main methodologies in use, one based on antigen-antibody interaction and the other based on amplified nucleic acids. The most commonly used nucleic acid markers are mutations or alterations in tumor DNA (tumor-specific markers) or differentially expressed mRNA (tissue-specific markers). Many reports and reviews have been published on the assessment of minimal residual disease by molecular markers, showing either positive or negative clinical correlations. One of the main reasons for these contradictory findings is the technical difficulty in finding the small numbers of tumor cells in the large number of normal cells, which necessitates sensitivities of the assays up to 1 tumor cell in 2 x 10(7) normal cells. These assays often are complex, demand considerable experience, and usually are laborious. In this review, we will address a number of the technical issues related to molecular assays for tumor cell detection that make use of nucleic acids as markers. Many difficulties in data interpretation are at least in part because of technical details that might have been solved by the incorporation of one or more appropriate controls. We hope that this review clarifies a number of these issues and help clinicians and investigators interested in this field to understand and weigh the contradictory findings in the published studies. This will help move the field forward and facilitate clinical implementation.