The cross linker between the hyaluronic acid molecules (cross linked HA Fillers) should be two part per million, if it is more than this it could be carcinogenic
All the fillers in the market are non carcinogenic since they fulfil this criteria
Based on the following link a rare case of lymphoma in a patient with a history of foreign body injection indicated that practitioners must be aware that long-standing chronic inflammation resulting from dermal filler injections can trigger lymphoma development.
Article B-Cell Lymphoma in a Patient With a History of Foreign Body Injection