Let’s put the facts together : one article of the NY Times providing a long, very long description of poaching in Vietnam, blaming the socialist regime and its corruption, pointing actually to poaching in the northern area :

2. the Leizhou 2018 sodium fast reactor explosion :

So the content of the core was carried by the hurricane, up to an actual “dense central overcast” noted by weather specialists in that hurricane, i.e. the cloud that landed mostly onto northern Vietnam. An area already contaminated with massive amounts of depleted uranium in the Vietnam war, intentionally (since all antitank weapons use small amount of nuclear fission and need no use of depleted uranium to penetrate, even a veteran French Army general, Pierre Marie Gallois said massive use of depleted uranium is a crime against humanity, in 1995).

Simple to understand, isn’t it ?
Stomach cancer is just taken as a keyword for a much wider array of symptoms – read my paper – the bottom part of the body is usually more affected because these are heavy particulates of dust.