Genomic Instability, DNA Alterations and Tumor Eosinophilic Expression in Head and Neck Squamous Cell Carcinoma

The progression of normal cells to invasive tumor cells has been attributed to the acquisition of numerous mutations in the genome; genomic instability (GI) facilitates the accumulation of these mutations. To study the GI in head and neck squamous cell carcinoma (HNSCC), the genomic instability index (GII) was examined; chromosomal gains and losses were evaluated by array comparative genomic hybridization (aCGH), which were confirmed by fluorescence in situ hybridization (FISH). Histopathological eosinophilic infiltrate (Eos Infil), as an adjunct measure of tumor invasiveness, was also considered and compared to GI.

Inter-simple sequence repeat PCR (ISSR-PCR) was utilized to determine the GII (a quantitative estimate of the relative overall genomic damage). GII was measured in 26 pairs of tumor and normal HNSCC samples. Array CGH was conducted using bacterial artificial chromosome (BAC) clones to evaluate amplifications and deletions (n=20 tumor), and confirmation of the specific changes was made by FISH analysis. Histopathological evaluation of Eos Infil for all samples was performed to calculate the eosinophilic index (EI). This was accomplished by observing Eos Infil in neoplastic tissue and at the tumor/normal tissue interface.

GI was evident in 25 of the 26 tumors. The GIIs ranged from 0 to 5.3% with a mean of 2.8% (similar to the results reported for colorectal and thyroid carcinomas). GIIs were higher in tumors of the oral cavity (OC) than in tumors from other subsites of HNSCC (p=0.05). Chromosomal alterations were identified by array CGH on chromosomes 8, 11 and 17, but consistent amplifications were observed on (8q21.3-23.5) in 80% of the tumors. These changes were confirmed using FISH analysis. There was an association between increased GI and rising EI, but this did not achieve statistical significance (p>0.05).

HNSCC exhibits a similar degree of GI to that previously reported in colorectal and thyroid malignancies. The higher GI identified in OC tumors could be explained by a greater degree of the damage from environmental carcinogens (smoke, diet and alcohol) to the first station of the areodigestive tract. Consistent amplification at the specific loci of 8q might be attributed to mutations in various genes, such as SHAX3 (Snf7 homolog, associated with Alix 3, involved in apoptosis and endocytosis) and E2F5 (transcription factor 5 that interacts with tumor suppressor proteins). EI was not associated with age, sex, site or stage of tumor in established cases. Further work up will be necessary to explain these results.