Altered p53 in microdissected, metachronous, premalignant and malignant oral lesions from the same patients

The prognostic significance of allelic imbalance at key chromosomal loci in oral cancer

Forty-eight primary oral squamous cell carcinomas (SCC) were screened for allelic imbalance (AI) at 3p24-26, 3p21, 3p13, 8p21-23, 9p21, 9q22 and within the Rb, p53 and DCC tumour suppressor genes. AI was detected at all TNM stages with stage 4 tumours showing significantly more aberrations than stage 1-3. A factional allelic loss (FAL) score was calculated for all tumours and a high score was associated with development of local recurrence (P = 0.033) and reduced survival (P = 0.0006). AI at one or more loci within the 3p24-26, 3p21, 3p13 and 9p21 regions or within the THRB and DCC genes was associated with reduced survival. The hazard ratios for survival analysis revealed that patients with AI at 3p24-26, 3p13 and 9p21 have an approximately 25 times increase in their mortality rate relative to a patient retaining heterozygosity at these loci. AI at specific pairs of loci, D3S686 and D9S171 and involving at least two of D3S1296, DCC and D9S43, was a better predictor of prognosis than the FAL score or TNM stage. These data suggest that it will be possible to develop a molecular staging system which will be a better predict of outcome than conventional clinicopathological features as the molecular events represent fundamental biological characteristics of each tumour.

The prognostic significance of allelic imbalance at key chromosomal loci in oral cancer

Forty-eight primary oral squamous cell carcinomas (SCC) were screened for allelic imbalance (AI) at 3p24-26, 3p21, 3p13, 8p21-23, 9p21, 9q22 and within the Rb, p53 and DCC tumour suppressor genes. AI was detected at all TNM stages with stage 4 tumours showing significantly more aberrations than stage 1-3. A factional allelic loss (FAL) score was calculated for all tumours and a high score was associated with development of local recurrence (P = 0.033) and reduced survival (P = 0.0006). AI at one or more loci within the 3p24-26, 3p21, 3p13 and 9p21 regions or within the THRB and DCC genes was associated with reduced survival. The hazard ratios for survival analysis revealed that patients with AI at 3p24-26, 3p13 and 9p21 have an approximately 25 times increase in their mortality rate relative to a patient retaining heterozygosity at these loci. AI at specific pairs of loci, D3S686 and D9S171 and involving at least two of D3S1296, DCC and D9S43, was a better predictor of prognosis than the FAL score or TNM stage. These data suggest that it will be possible to develop a molecular staging system which will be a better predict of outcome than conventional clinicopathological features as the molecular events represent fundamental biological characteristics of each tumour.

New insights into p53 protein stabilisation in oral squamous cell carcinoma

p53 is a transcription factor which regulates cell proliferation and apoptosis to prevent division of potentially malignant cells. In many tumours mutation of the p53 gene leads to stabilisation of this protein which can be detected by immunohistochemistry (IHC). However, there are many reports describing detection of p53 by IHC in the absence of gene mutation, and in these cases other factors stabilise p53. To shed light on the mechanisms which permit detection of this protein in these mutation-negative cases we have examined 45 primary oral squamous cell carcinomas (SCCs) by IHC and gene sequencing for p53 (exons 4-8) and related the results to a FAL score (determined using microsatellite assay and expressing the number of loci showing allelic imbalance as a fraction of the total number of informative markers for each case). We also investigated the pattern of MDM2 expression in these tumours. High levels of p53 protein were detected in 24/45 cases and point mutations involving exons 4-9 were seen in 11 cases. A further four cases harboured deletions or a stop codon. For 6/48 cases there was concordance of AI within the p53 gene and mutation. However nine cases showed p53 mutation only and 5 AI without mutation, suggesting that oral tumours frequently retain one normal p53 allele. Detection of p53 by IHC correlated strongly with the FAL score. Thus whilst it is possible that some tumours harbour p53 mutations outside the open reading frames examined, or are missed due to sequencing a mixture of normal and tumour tissue, a subgroup of tumours may express high levels of wild-type p53 as a reflection of the high FAL score and ongoing genomic stress. Levels of MDM2 transcripts and protein were similar in all SCCs examined. However, MDM2 may be non-functional, or there may be defects affecting other important regulatory proteins in tumours which which express wild type p53 protein.

p53 immunostaining and image cytometry DNA analysis in precancerous and cancerous squamous epithelial lesions of the larynx

BACKGROUND

Squamous epithelial cancer can develop from progressive epithelial changes connoted dysplasias. Histopathologic evaluation/grading of these lesions is difficult and gives poor information concerning the risk for progression to cancer. Squamous cell carcinoma of the head and neck (SCCHN) frequently show p53 alteration and DNA-ploidy aberration. Could these markers be used as indicators for malignancy risk in the larynx?

METHODS

Immunohistochemical staining (IHC), with the CM-1 antibody against p53, and image cytometry (ICM) DNA analysis were performed in 60 lesions from 12 patients--and 21 controls--who were initially seen with laryngeal lesions prior to cancer in situ (cis) or invasive cancer diagnosis at the same site.

RESULTS

All but one of the invasive cancers, and 77% of the lesions which preceded cancer or cancer in situ, showed positive p53 immunostaining, as compared with only 10% of the controls. All but one of the invasive cancer lesions, and 77% of the precancerous lesions, showed aberrant DNA-ploidy results, whereas all controls were diploid. When DNA and p53 analysis were combined, only one of the lesions preceding cis or invasive cancer was negative.

CONCLUSIONS

Both p53 immunoreactivity and DNA-ploidy aberration appear to be early events in the multistep process of squamous epithelial carcinogenesis. Immunohistochemical staining p53 analysis and ICM DNA analysis does increase the diagnostic sensitivity for cancerous and true precancerous lesions in the larynx.

The role of p53 tumor suppressor gene in human head and neck tumorigenesis

Molecular genetics has led to new insights into diagnosis and treatment of human cancer. The alterations of tumor suppressor genes like retinoblastoma, p53 and others may have an important role in tumorigenesis. Mutations of p53 have been found in a majority of human malignancies including head and neck cancer. The distribution of p53 is different between types of tumors, suggesting environmental exposure as a cause active factor. The p53 mutation in head and neck tumors is an early event and appears to have a hot spot region at codons 238-248. While mutation and loss of heterozygosity at p53 are important in the genesis of head and neck cancer, other mechanisms such as binding of viral and cellular proteins to p53 are also likely to play a role.