Allergen immunotherapy (AIT) is currently more than 100 years old. It is considered an evidence-based efficacious immune therapeutical treatment. It is at this time the only causative treatment for allergic respiratory and venom allergic diseases. Though clinical indications for AIT are well established, clinical contraindications to AIT differ among several guidelines. Regarding malignant neoplasia, traditionally, it has been considered as a relative or absolute contraindication with the concern that AIT might stimulate tumour growth even though pathogenic impact of AIT in cancer is not well understood. Furthermore, this contraindication is often based on observational case series, or case reports, with little real evidence-based data. Therefore, should cancer still be contemplated as an absolute contraindication for AIT?