PLK1 and non-small cell lung carcinoma: To date, PLK mRNA expression has been studied in a few types of carcinoma such as non-small cell lung carcinoma, squamous cell carcinoma of the head and neck, gastric carcinoma, and oesophageal carcinoma (Wolf et al, 1997; Knecht et al, 1999; Tokumitsu et al, 1999).