In addition to E antigens, serum levels of matrix metalloproteinases (MMP1, 2 and 9) have been studied in oropharyngeal, laryngeal and hypopharyngeal carcinoma by Kalfert et al. and found not to serve as suitable prognostic tumour markers in these cancers.14 MMP1 expression was described as being significantly influenced by smoking and p16 expression. This evidence concerns the gene CDKN2A and neoplasm.