Hi! welcome to HCM! Its good that after treatment nothing was seen in PET scan. Recurrence is strongly related to stage of tumour which in turn depends on size and extent of primary tumour,presence of cancer cells in regional or distant lymph nodes and spread of cancer cells to other organs. In occurence of these cancers both environmental (diet) and genetic factors play role.It is observed in populations with a Western type diet, i.e. highly caloric food rich in animal fat , meat consumption, smoking and alcohol con- sumption are risk factors. To prevent it vegetable consumption, and physical activity are important and fibre may have a protective role. I sincerely hope this information is useful for you!