Medically speaking such a complication would not happen due to vaccine. It was simply bad luck.
The concerns of allowing the Pfizer vaccine for use mostly boils down to efficiency concerns and nothing else.
There is no proof that the Pfizer vaccine has greater or unusual side effects, although the moderna one does, hence it is not preferred for old individuals, yet these are heart disease complications, not ones related to cancer.
There is no thing such as "GMO vaccine", all vaccines use gene modification. For Sinovac vaccine, it uses quite literally a genetically modified whole covid virus which has its harmful parts removed, whereas for Pfizer vaccine it uses a mimicked sequence of the body's own response against a part of covid antigen. In that regard, the latter can be seen as more "natural" as far as vaccines go, but we are not striving for a more natural response but rather a more effective one. And proven by number of covid cases as well as select studies, one can see that the former has significant advantages.