Dormant cancer cells that survive anti-cancer therapy can lead to cancer recurrence and disseminated metastases that prove fatal in most cases. Recently, specific dormant polyploid giant cancer cells (PGCC) have drawn the investigators' attention because of their association with the clinical risk of nasopharyngeal carcinoma (NPC) recurrence, as demonstrated by previous clinical data. In study, the investigators report the biological properties of PGCC, and reveal that autophagy is a critical mechanism of PGCC induction. Moreover, pharmacological inhibition of autophagy greatly impaired PGCC formation, significantly suppressing metastasis and improving survival in a mouse model. Mechanistically, chemotherapeutic drugs partly damaged mitochondria, and activated autophagy to promote PGCC formation. High numbers of PGCCs correlated with shorter recurrence time and worse survival outcomes in NPC patients. Collectively, these findings suggest a therapeutic approach of targeting dormant PGCCs in cancer. Pretreatment with an autophagy inhibitor (HCQ) before chemotherapy and radiotherapy could prevent formation of therapy-induced dormant polyploid giant cancer cells, thereby reducing recurrence and metastasis of nasopharyngeal carcinoma.