To my knowledge, there is no reputable literature available that points to long term or chronic use of sodium chloride as a cause of malignancy. The chronic use of a hypertonic solution such as NaCl could cause damage to the cell membrane and thus induce a change which could possible cause recognition by the immune system as "foreign". However, the long term use of NaCl and its activity on the DNA and/or nuclear membrane is not addressed sufficiciently in the literature to answer such a question. Why do you pose such a question?

I don't know how relevant this might be to the question you posed but I've just been reading a paper which demonstrated the effect of high NaCl [300mM] compared with [10mM] on the basal G-protein activity of 5HT receptors. Low NaCl inhibited basal G-protein activity (newman-tancredi et al, BJPharm 2003). Asynchronous G-protein activation can lead to the oncogenic transformation of different cell types (Radhika & Dhanasekaran, Oncogene, 2001).