Before pollen grains are considered for cancer treatment each pollen grain must be well differentiated and classified as all known pollen grains only then each one has to be studied individually and systemically tried in lab for the different cancers of different many animals when these sutdies reach to certain maturity approved by medical sciences then it can progress to human studies !
People who are allergic to pollen grains will definitely have side effects and risk factors even though pollen grains possess significant anti-cancer potential.