PLK1 and squamous cell carcinoma: This hypothesis matches well with observations that PLK1 expression is a survival parameter in oesophageal carcinoma (Tokumitsu et al, 1999), lung carcinoma (Wolf et al, 1997) and squamous cell carcinoma of head and neck (Knecht et al, 1999), and serves as a marker for metastatic disease in malignant melanoma (Kneisel et al, 2002).