PPL and carcinoma of esophagus: In patients with a history of smoking and who present with hyper-methylation of oesophageal mucosa, DNA methylation of PPL promoter sequences leads to reduced expression of PPL and have been linked to the development of oesophageal squamous cell carcinoma [70], suggesting that loss of PPL may be one of the early events in the progression of oesophageal cancer.