LCK and neoplasm: It has been shown that decreased or absent expression of the ζ chain results in signalling defects in TIL or tumour-associated lymphocytes (TAL), such as altered expression of the tyrosine kinase p56lck and a decreased ability to mobilise intracellular Ca2+ in response to activation signals (Mizoguchi et al, 1992; Finke et al, 1993; Nakagomi et al, 1993; Lai et al, 1996; Rabinowich et al, 1996).