The role of chromosome 22 in the progression of head and neck squamous cell carninoma

Condon, Luke Thomas

Abstract

Head and neck squamous cell carcinoma (HNSCC) is one o f the ten most frequent cancers in the world. Despite advances in surgery, radiotherapy and chemotherapy over the last 30 years, there has been little improvement in the mortality rate from this disease. HNSCC remains a leading cause of cancer death, particularly once it has metastasised to the regional lymph nodes. The presence of metastatic cervical lymphadenopathy at the time of diagnosis reduces the likelihood of 5-year survival by 50%.

Preliminary comparative genomic hybridisation (CGH) work in our laboratory, aimed at identifying genetic markers of metastasis, suggested that amplification of chromosome arm 22q may be important in enabling malignant cells to metastasise. Overamplification of 22q was observed in 5/17 (29%) lymph node metastases (LNM) compared with none of their matched primary tumours. In a further group of 12 non-metastasising primary tumours there was no evidence of either gross deletion or amplification of 22q, supporting its unique association with metastasis. However, a literature search revealed two other studies that had identified significant aberration of 22q in primary head and neck cancers, as opposed to metastases.

Thus two contrasting bodies o f evidence exist for the role o f a putative oncogene on 22q in HNSCC. Two studies support a role during initial tumorigenesis, whilst another supports a role in the process of lymph node metastasis.

The aim of this thesis was to determine which of these two roles for 22q is more likely in HNSCC, and to narrow the search for the putative oncogene in question. For patients with HNSCC, microsatellite markers were used to investigate allele imbalance (Al) along 22q and in doing so to construct a high resolution AI map of this chromosome arm.

The 9 microsatellite markers selected covered approximately 25Mb (72%) of 22q, spanning 22q11.23 to 22ql3.31. A series of 28 patients with nodal metastases from laryngeal or hypopharyngeal squamous cell carcinoma were selected. DNA was extracted from normal tissue and primary tumour for each patient, and microsatellite marker analysis performed. The microsatellite loci examined, and rates of AI were as follows: D22S420 (11%), D22S539 (25%), D22S117 (4%), D22S315 (0%), D22S1163 (15%), D22S280 (20%), D22S277 (15%), D22S283 (11%) and D22S1169 (0%). Overall there was no significant AI (mean rate AI = 8.2%), thus confirming our null hypothesis based on our CGH results that there would be no significant AI between the normal and tumour DNA samples. This finding would tend to refute a role for 22q in initial tumorigenesis, and future work will examine the corresponding lymph node metastases for AI. Microsatellite instability was a very infrequent event (1% cases), suggesting that HNSCC does not primarily arise through defects in the mismatch repair system.

The role of 22q at the protein level was also examined using immunohistochemistry. Gene databases were searched for potential candidate oncogenes, which may be responsible for the metastatic competence of head and neck tumours with 22q amplification. The matrix metalloproteinase (MMP) Stromelysin III (MMP-11) is encoded by a gene that resides on 22ql 1.2. Evidence from studies of other malignancies supports a role for MMP-11 in the initial invasive stages of the metastatic cascade. The second part of the thesis tested the hypothesis that there would be no difference in MMP-11 expression between normal tissue and primary tumour, but that there would be increased MMP-11 expression in lymph node metastases. This was found to be the case, with a significantly higher level of MMP-11 detected in the lymph node metastases (p=0.01). MMP-11 may therefore be a putative proto-oncogene responsible for allowing head and neck squamous cell carcinoma cells to metastasise.

The sequencing results do not support a specific role for aberrations o f chromosome 22q in initial head and neck tumorigenesis. They also exclude defects in the mismatch repair system as a significant mechanism of tumorigenesis in head and neck cancer. The immunostaining results do support a role for MMP-11 overexpression in the progression from primary tumour to metastasis. It remains to be seen whether the observed overexpression of MMP-11 in metastatic carcinoma cells is due to amplification o f chromosome 22q. This work will be continued, with microsatellite analysis o f the matched lymph node metastases. These findings will increase our understanding o f the molecular mechanisms o f metastasis, and hopefully provide novel therapeutic targets.

Citation

Condon, L. T. (2003). The role of chromosome 22 in the progression of head and neck squamous cell carninoma. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4223891

• Thesis Type: Thesis
• Deposit Date: Feb 9, 2022
• Publicly Available Date: Feb 24, 2023
• Keywords: Medicine
• Public URL: https://hull-repository.worktribe.com/output/4223891
• Additional Information: Postgraduate Medical School, The University of Hull
• Award Date: Dec 1, 2003