XJhues, looking at the linked study, they find no statistically sig relationship between nitrate and nitrite consumption and any cancers. They did find a stat sig relationship between NMDA intake and colorectal cancer, but not with any other of the cancers. The main sources of NDMA in the study population were smoked/salted fish, cured meats/sausages and beer, but only smoked/salted fish showed a stat sig relationship with colorectal cancer. Fresh fish did not. THey do say that previous cohort studies HAVE found stat sig relationships with beer intake and cured meat products and colorectal cancer. I don't have time today to chase down all the references though and inspect each study beyond this one but I suspect these others are also epidemiological, which means they are inherently weak and don't/can't show causation. This study only found a stastistical link with NMDA but not with nitrates or nitrites.
Ironically, they also noted that over 90 percent of nitrate intake in the study population came from vegetable intake (77 mg from all sources). So cutting meat consumption may not result in decreased nitrate intake if you end up eating more vegetables. Wheras nitrite consumption primarily from meat sources only constitued 5.3 mg. But neither were stat sig linked with cancer in the study.
Overall, interesting and something to consider and be wary of, but exact lines of causation and mechanism are still not well understood. Also, interesting, they said that due to changed processing methods, levels of NMDA vary wildly between different products and overall have been greatly reduced in recent years.